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Author: wave-gbt

Database/177. Nth Highest Salary.md

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+Write a SQL query to get the nth highest salary from the Employee table.
+
+```
++----+--------+
+| Id | Salary |
++----+--------+
+| 1  | 100    |
+| 2  | 200    |
+| 3  | 300    |
++----+--------+
+```
+For example, given the above Employee table, the nth highest salary where n = 2 is 200. If there is no nth highest salary, then the query should return null.
+
+```
++------------------------+
+| getNthHighestSalary(2) |
++------------------------+
+| 200                    |
++------------------------+
+```
+**SQL**
+```mysql
+CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
+BEGIN
+    set N=N-1;
+  RETURN (
+      # Write your MySQL query statement below.
+    select distinct Salary from Employee order by Salary desc limit N,1
+  );
+END
+```

algorithm/14. Longest Common Prefix.md

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+Write a function to find the longest common prefix string amongst an array of strings.
+
+**code**
+
+```java
+class Solution {
+    public String longestCommonPrefix(String[] strs) {
+        
+         if(strs.length==0)  
+            return "";  
+        String prefix =strs[0];  
+        for(int i = 1;i<strs.length;i++){  
+            while(strs[i].indexOf(prefix) != 0){  
+                prefix = prefix.substring(0,prefix.length()-1);  
+  
+            }  
+        }     
+        return prefix;  
+    }
+}
+```

algorithm/20. Valid Parentheses.md

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+Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
+
+The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.
+
+**code**
+```java
+class Solution {
+    public boolean isValid(String s) {
+        Stack<Integer> p = new Stack<>();
+        for(int i = 0; i < s.length(); i++) {
+            int q = "(){}[]".indexOf(s.substring(i, i + 1));
+            if(q % 2 == 1) {
+                if(p.isEmpty() || p.pop() != q - 1) return false;
+            } else p.push(q);
+        }
+        return p.isEmpty();
+    }
+}
+```

algorithm/21. Merge Two Sorted Lists.md

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+Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
+
+**Example:**
+
+```
+Input: 1->2->4, 1->3->4
+Output: 1->1->2->3->4->4
+```
+```
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        if(l1 == null) {
+            return l2;
+        }
+		if(l2 == null){
+            return l1;
+        } 
+		if(l1.val < l2.val){
+			l1.next = mergeTwoLists(l1.next, l2);
+			return l1;
+		} else{
+			l2.next = mergeTwoLists(l1, l2.next);
+			return l2;
+		}
+        
+    }
+}
+```

algorithm/27. Remove Element.md

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+Given an array and a value, remove all instances of that value in-place and return the new length.
+
+Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
+
+The order of elements can be changed. It doesn't matter what you leave beyond the new length.
+
+**Example:**
+```
+Given nums = [3,2,2,3], val = 3,
+
+Your function should return length = 2, with the first two elements of nums being 2.
+
+```
+
+**code**
+```java
+class Solution {
+    public int removeElement(int[] nums, int val) {
+        int i = 0;
+    int n = nums.length;
+    while (i < n) {
+        if (nums[i] == val) {
+            nums[i] = nums[n - 1];
+            // reduce array size by one
+            n--;
+        } else {
+            i++;
+        }
+    }
+    return n;
+    }
+}
+
+```

leetcode-practice.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module type="WEB_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$" />
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>