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‎src/main/java/g3601_3700/s3673_find_zombie_sessions/readme.md

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3673\. Find Zombie Sessions
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Hard
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Table: `app_events`
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+------------------+----------+
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| Column Name | Type |
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+------------------+----------+
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| event_id | int |
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| user_id | int |
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| event_timestamp | datetime |
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| event_type | varchar |
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| session_id | varchar |
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| event_value | int |
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+------------------+----------+
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event_id is the unique identifier for this table.
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event_type can be app_open, click, scroll, purchase, or app_close.
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session_id groups events within the same user session.
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event_value represents: for purchase - amount in dollars, for scroll - pixels scrolled, for others - NULL.
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Write a solution to identify **zombie sessions, **sessions where users appear active but show abnormal behavior patterns. A session is considered a **zombie session** if it meets ALL the following criteria:
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* The session duration is **more than** `30` minutes.
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* Has **at least** `5` scroll events.
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* The **click-to-scroll ratio** is less than `0.20` .
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* **No purchases** were made during the session.
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Return _the result table ordered by_ `scroll_count` _in **descending** order, then by_ `session_id` _in **ascending** order_.
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The result format is in the following example.
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**Example:**
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**Input:**
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app\_events table:
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+----------+---------+---------------------+------------+------------+-------------+
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| event_id | user_id | event_timestamp | event_type | session_id | event_value |
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+----------+---------+---------------------+------------+------------+-------------+
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| 1 | 201 | 2024-03-01 10:00:00 | app_open | S001 | NULL |
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| 2 | 201 | 2024-03-01 10:05:00 | scroll | S001 | 500 |
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| 3 | 201 | 2024-03-01 10:10:00 | scroll | S001 | 750 |
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| 4 | 201 | 2024-03-01 10:15:00 | scroll | S001 | 600 |
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| 5 | 201 | 2024-03-01 10:20:00 | scroll | S001 | 800 |
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| 6 | 201 | 2024-03-01 10:25:00 | scroll | S001 | 550 |
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| 7 | 201 | 2024-03-01 10:30:00 | scroll | S001 | 900 |
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| 8 | 201 | 2024-03-01 10:35:00 | app_close | S001 | NULL |
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| 9 | 202 | 2024-03-01 11:00:00 | app_open | S002 | NULL |
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| 10 | 202 | 2024-03-01 11:02:00 | click | S002 | NULL |
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| 11 | 202 | 2024-03-01 11:05:00 | scroll | S002 | 400 |
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| 12 | 202 | 2024-03-01 11:08:00 | click | S002 | NULL |
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| 13 | 202 | 2024-03-01 11:10:00 | scroll | S002 | 350 |
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| 14 | 202 | 2024-03-01 11:15:00 | purchase | S002 | 50 |
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| 15 | 202 | 2024-03-01 11:20:00 | app_close | S002 | NULL |
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| 16 | 203 | 2024-03-01 12:00:00 | app_open | S003 | NULL |
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| 17 | 203 | 2024-03-01 12:10:00 | scroll | S003 | 1000 |
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| 18 | 203 | 2024-03-01 12:20:00 | scroll | S003 | 1200 |
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| 19 | 203 | 2024-03-01 12:25:00 | click | S003 | NULL |
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| 20 | 203 | 2024-03-01 12:30:00 | scroll | S003 | 800 |
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| 21 | 203 | 2024-03-01 12:40:00 | scroll | S003 | 900 |
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| 22 | 203 | 2024-03-01 12:50:00 | scroll | S003 | 1100 |
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| 23 | 203 | 2024-03-01 13:00:00 | app_close | S003 | NULL |
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| 24 | 204 | 2024-03-01 14:00:00 | app_open | S004 | NULL |
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| 25 | 204 | 2024-03-01 14:05:00 | scroll | S004 | 600 |
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| 26 | 204 | 2024-03-01 14:08:00 | scroll | S004 | 700 |
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| 27 | 204 | 2024-03-01 14:10:00 | click | S004 | NULL |
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| 28 | 204 | 2024-03-01 14:12:00 | app_close | S004 | NULL |
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+----------+---------+---------------------+------------+------------+-------------+
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**Output:**
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+------------+---------+--------------------------+--------------+
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| session_id | user_id | session_duration_minutes | scroll_count |
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+------------+---------+--------------------------+--------------+
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| S001 | 201 | 35 | 6 |
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+------------+---------+--------------------------+--------------+
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**Explanation:**
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* **Session S001 (User 201)**:
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* Duration: 10:00:00 to 10:35:00 = 35 minutes (more than 30)
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* Scroll events: 6 (at least 5)
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* Click events: 0
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* Click-to-scroll ratio: 0/6 = 0.00 (less than 0.20)
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* Purchases: 0 (no purchases)
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* S001 is a zombie session (meets all criteria)
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* **Session S002 (User 202)**:
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* Duration: 11:00:00 to 11:20:00 = 20 minutes (less than 30)
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* Has a purchase event
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* S002 is not a zombie session
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* **Session S003 (User 203)**:
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* Duration: 12:00:00 to 13:00:00 = 60 minutes (more than 30)
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* Scroll events: 5 (at least 5)
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* Click events: 1
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* Click-to-scroll ratio: 1/5 = 0.20 (not less than 0.20)
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* Purchases: 0 (no purchases)
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* S003 is not a zombie session (click-to-scroll ratio equals 0.20, needs to be less)
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* **Session S004 (User 204)**:
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* Duration: 14:00:00 to 14:12:00 = 12 minutes (less than 30)
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* Scroll events: 2 (less than 5)
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* S004 is not a zombie session
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The result table is ordered by scroll\_count in descending order, then by session\_id in ascending order.

‎src/main/java/g3601_3700/s3673_find_zombie_sessions/script.sql

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# Write your MySQL query statement below
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# #Hard #Database #2025_09_07_Time_278_ms_(100.00%)_Space_0.0_MB_(100.00%)
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SELECT
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session_id,
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user_id,
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TIMESTAMPDIFF(MINUTE, MIN(event_timestamp), MAX(event_timestamp)) AS session_duration_minutes,
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SUM(CASE WHEN event_type = 'scroll' THEN 1 ELSE 0 END) AS scroll_count -- NOSONAR
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FROM
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app_events
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GROUP BY
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session_id,
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user_id
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HAVING
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TIMESTAMPDIFF(MINUTE, MIN(event_timestamp), MAX(event_timestamp)) > 30
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AND SUM(CASE WHEN event_type = 'scroll' THEN 1 ELSE 0 END) > 4 -- NOSONAR
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AND (
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CAST(SUM(CASE WHEN event_type = 'click' THEN 1 ELSE 0 END) AS DOUBLE) /
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NULLIF(SUM(CASE WHEN event_type = 'scroll' THEN 1 ELSE 0 END), 0) -- NOSONAR
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) < 0.2
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AND SUM(CASE WHEN event_type = 'purchase' THEN 1 ELSE 0 END) = 0
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ORDER BY
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scroll_count DESC,
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session_id ASC;

‎src/main/java/g3601_3700/s3674_minimum_operations_to_equalize_array/Solution.java

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package g3601_3700.s3674_minimum_operations_to_equalize_array;
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// #Easy #Weekly_Contest_466 #2025_09_07_Time_1_ms_(100.00%)_Space_43.98_MB_(100.00%)
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public class Solution {
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public int minOperations(int[] nums) {
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for (int num : nums) {
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if (num != nums[0]) {
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return 1;
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}
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}
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return 0;
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}
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}

‎src/main/java/g3601_3700/s3674_minimum_operations_to_equalize_array/readme.md

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3674\. Minimum Operations to Equalize Array
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Easy
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You are given an integer array `nums` of length `n`.
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In one operation, choose any subarray `nums[l...r]` (`0 <= l <= r < n`) and **replace** each element in that subarray with the **bitwise AND** of all elements.
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Return the **minimum** number of operations required to make all elements of `nums` equal.
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A **subarray** is a contiguous **non-empty** sequence of elements within an array.
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**Example 1:**
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**Input:** nums = [1,2]
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**Output:** 1
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**Explanation:**
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Choose `nums[0...1]`: `(1 AND 2) = 0`, so the array becomes `[0, 0]` and all elements are equal in 1 operation.
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**Example 2:**
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**Input:** nums = [5,5,5]
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**Output:** 0
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**Explanation:**
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`nums` is `[5, 5, 5]` which already has all elements equal, so 0 operations are required.
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**Constraints:**
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* `1 <= n == nums.length <= 100`
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* <code>1 <= nums[i] <= 10<sup>5</sup></code>

‎src/main/java/g3601_3700/s3675_minimum_operations_to_transform_string/Solution.java

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package g3601_3700.s3675_minimum_operations_to_transform_string;
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// #Medium #Weekly_Contest_466 #2025_09_14_Time_5_ms_(100.00%)_Space_47.93_MB_(95.06%)
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public class Solution {
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public int minOperations(String s) {
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int n = s.length();
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int ans = 0;
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for (int i = 0; i < n; i++) {
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final char c = s.charAt(i);
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if (c != 'a') {
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int ops = 'z' - c + 1;
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if (ops > ans) {
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ans = ops;
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}
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if (ops == 25) {
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break;
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}
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}
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}
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return ans;
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}
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}

‎src/main/java/g3601_3700/s3675_minimum_operations_to_transform_string/readme.md

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3675\. Minimum Operations to Transform String
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Medium
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You are given a string `s` consisting only of lowercase English letters.
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You can perform the following operation any number of times (including zero):
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* Choose any character `c` in the string and replace **every** occurrence of `c` with the **next** lowercase letter in the English alphabet.
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Return the **minimum** number of operations required to transform `s` into a string consisting of **only** `'a'` characters.
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**Note:** Consider the alphabet as circular, thus `'a'` comes after `'z'`.
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**Example 1:**
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**Input:** s = "yz"
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**Output:** 2
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**Explanation:**
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* Change `'y'` to `'z'` to get `"zz"`.
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* Change `'z'` to `'a'` to get `"aa"`.
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* Thus, the answer is 2.
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**Example 2:**
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**Input:** s = "a"
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**Output:** 0
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**Explanation:**
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* The string `"a"` only consists of `'a'` characters. Thus, the answer is 0.
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**Constraints:**
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* <code>1 <= s.length <= 5 * 10<sup>5</sup></code>
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* `s` consists only of lowercase English letters.

‎src/main/java/g3601_3700/s3676_count_bowl_subarrays/Solution.java

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package g3601_3700.s3676_count_bowl_subarrays;
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// #Medium #Weekly_Contest_466 #2025_09_14_Time_2_ms_(100.00%)_Space_58.91_MB_(69.85%)
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public class Solution {
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public long bowlSubarrays(int[] nums) {
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int n = nums.length;
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int res = n;
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int pre = 0;
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for (int a : nums) {
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if (a > pre) {
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res--;
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pre = a;
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}
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}
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pre = 0;
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for (int i = n - 1; i >= 0; i--) {
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if (nums[i] > pre) {
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res--;
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pre = nums[i];
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}
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}
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return res + 1L;
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}
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}

‎src/main/java/g3601_3700/s3676_count_bowl_subarrays/readme.md

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3676\. Count Bowl Subarrays
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Medium
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You are given an integer array `nums` with **distinct** elements.
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A subarray `nums[l...r]` of `nums` is called a **bowl** if:
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* The subarray has length at least 3. That is, `r - l + 1 >= 3`.
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* The **minimum** of its two ends is **strictly greater** than the **maximum** of all elements in between. That is, `min(nums[l], nums[r]) > max(nums[l + 1], ..., nums[r - 1])`.
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Return the number of **bowl** subarrays in `nums`.
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**Example 1:**
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**Input:** nums = [2,5,3,1,4]
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**Output:** 2
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**Explanation:**
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The bowl subarrays are `[3, 1, 4]` and `[5, 3, 1, 4]`.
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* `[3, 1, 4]` is a bowl because `min(3, 4) = 3 > max(1) = 1`.
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* `[5, 3, 1, 4]` is a bowl because `min(5, 4) = 4 > max(3, 1) = 3`.
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**Example 2:**
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**Input:** nums = [5,1,2,3,4]
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**Output:** 3
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**Explanation:**
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The bowl subarrays are `[5, 1, 2]`, `[5, 1, 2, 3]` and `[5, 1, 2, 3, 4]`.
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**Example 3:**
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**Input:** nums = [1000000000,999999999,999999998]
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**Output:** 0
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**Explanation:**
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No subarray is a bowl.
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**Constraints:**
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* <code>3 <= nums.length <= 10<sup>5</sup></code>
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* <code>1 <= nums[i] <= 10<sup>9</sup></code>
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* `nums` consists of distinct elements.

‎src/main/java/g3601_3700/s3677_count_binary_palindromic_numbers/Solution.java

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package g3601_3700.s3677_count_binary_palindromic_numbers;
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// #Hard #Weekly_Contest_466 #2025_09_07_Time_1_ms_(100.00%)_Space_40.86_MB_(100.00%)
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public class Solution {
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private long makePalin(long left, boolean odd) {
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long ans = left;
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if (odd) {
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left = left >> 1;
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}
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while (left > 0) {
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ans = (ans << 1) | (left & 1);
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left = left >> 1;
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}
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return ans;
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}
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public int countBinaryPalindromes(long n) {
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if (n == 0) {
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return 1;
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}
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int len = 64 - Long.numberOfLeadingZeros(n);
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long count = 1;
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for (int i = 1; i < len; i++) {
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int half = (i + 1) / 2;
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count += 1L << (half - 1);
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}
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int half = (len + 1) / 2;
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long prefix = n >> (len - half);
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long palin = makePalin(prefix, len % 2 == 1);
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count += (prefix - (1L << (half - 1)));
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if (palin <= n) {
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++count;
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}
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return (int) count;
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}
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}

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