chore: 候选题

Author: luzhipeng

134.gas-station.js

@@ -3,12 +3,59 @@
  *
  * [134] Gas Station
  */
+
+function getIndex(index, n) {
+  if (index > n - 1) {
+    return index - n;
+  }
+  return index;
+}
 /**
  * @param {number[]} gas
  * @param {number[]} cost
  * @return {number}
  */
 var canCompleteCircuit = function(gas, cost) {
+  // bad 时间复杂度O(n^2)
+  //   let remain = 0;
+  //   const n = gas.length;
+  //   for (let i = 0; i < gas.length; i++) {
+  //     remain += gas[i];
+  //     remain -= cost[i];
+  //     let count = 0;
+  //     while (remain >= 0) {
+  //       count++;
+  //       if (count === n) return i;
+  //       remain += gas[getIndex(i + count, n)];
+  //       remain -= cost[getIndex(i + count, n)];
+  //     }
+  //     remain = 0;
+  //   }
+  //   return -1;
+  // better solution 时间复杂度O(n)
+
+  const n = gas.length;
+  let total = 0;
+  let remain = 0;
+  let start = 0;
+
+  for(let i = 0; i < n; i++) {
+    total += gas[i];
+    total -= cost[i]
+
+    remain += gas[i];
+    remain -= cost[i];
 
-};
+    // 如果remain < 0, 说明从start到i走不通
+    // 并且从start到i走不通，那么所有的solution中包含start到i的肯定都走不通
+    // 因此我们重新从i + 1开始作为start
+    if (remain < 0) {
+        remain = 0;
+        start = i + 1;
+    }
+  }
+  // 事实上，我们遍历一遍，也就确定了每一个元素作为start是否可以走完一圈
 
+  // 如果cost总和大于gas总和，无论如何也无法走到终点
+  return total >= 0 ? start :  -1;
+};

14.longest-common-prefix.js

@@ -0,0 +1,44 @@
+/*
+ * @lc app=leetcode id=14 lang=javascript
+ *
+ * [14] Longest Common Prefix
+ */
+
+function isCommonPrefix(strs, middle) {
+  const prefix = strs[0].substring(0, middle);
+  for (let i = 1; i < strs.length; i++) {
+    if (!strs[i].startsWith(prefix)) return false;
+  }
+
+  return true;
+}
+/**
+ * @param {string[]} strs
+ * @return {string}
+ */
+var longestCommonPrefix = function(strs) {
+  // trie 解法
+  // 时间复杂度O(m) 空间复杂度O(m * n)
+
+  // tag: 二分法
+  // 时间复杂度 O(n*logm*logm)  空间复杂度O(1)
+  if (strs.length === 0) return "";
+  if (strs.length === 1) return strs[0];
+
+  let minLen = Number.MAX_VALUE;
+
+  for (let i = 0; i < strs.length; i++) {
+    minLen = Math.min(minLen, strs[i].length);
+  }
+
+  let low = 0;
+  let high = minLen;
+
+  while (low <= high) {
+    const middle = (low + high) >> 1;
+    if (isCommonPrefix(strs, middle)) low = middle + 1;
+    else high = middle - 1;
+  }
+
+  return strs[0].substring(0, (low + high) >> 1);
+};

227.basic-calculator-ii.js

@@ -8,29 +8,5 @@
  * @return {number}
  */
 var calculate = function(s) {
-  const chars = s.split('').filter(q => q);
-
-  const stack = [];
-  for(let c of chars) {
-    if (!isNaN(c)) {
-        stack.push(c);
-    } else {
-        const a  = stack.pop();
-        const b  = stack.pop();
-
-        if (c === '+') {
-            stack.push(b + a);
-        } else if (c === '-') {
-            stack.push(b - a);
-        } else if (c === '*') {
-            stack.push(b * a);
-        } else if (c === '/') {
-            stack.push(Math.floor(b / a));
-        }
-    }
-  }
-
-  return stack.pop();
-
+  // "3+2*2"
 };
-

300.longest-increasing-subsequence.js

@@ -8,7 +8,8 @@
  * @return {number}
  */
 var lengthOfLIS = function(nums) {
-  if (nums.length === 0) return 0;
+  // 时间复杂度O(n^2)
+  // if (nums.length === 0) return 0;
   //   const dp = Array(nums.length).fill(1);
   //   let max = 1;
 
@@ -25,4 +26,20 @@ var lengthOfLIS = function(nums) {
 
   // [ 10, 9, 2, 5, 3, 7, 101, 18 ]
   // [ 2, 3, 5, 7, 9, 10, 18, 101 ]
+
+  // 参考： https://leetcode.com/problems/longest-increasing-subsequence/discuss/74824/JavaPython-Binary-search-O(nlogn)-time-with-explanation
+  // const tails = [];
+  // for (let i = 0; i < nums.length; i++) {
+  //   let left = 0;
+  //   let right = tails.length;
+  //   while (left < right) {
+  //     const mid = left + (right - left) / 2; // 防止溢出
+  //     if (tails[mid] < nums[i]) left = mid + 1;
+  //     else right = mid;
+  //   }
+  //   // 说明nums[i] 比如tails中所有数字都大，我们直接push
+  //   if (right === tails.length) tails.push(nums[i]);
+  //   else tails[right] = nums[i]; // 否则我们修改tails[right]
+  // }
+  // return tails.length;
 };

84.largest-rectangle-in-histogram.js

@@ -32,27 +32,27 @@ var largestRectangleArea = function(heights) {
 
   // 社区中流行的一种解法: 单调栈,  在这里我们需要使用单调递增栈
   // 时间复杂度O(n) 空间复杂度O(n)
-  const ascStack = [];
-  let max = 0;
-  heights.push(0); // hack, 为了使最后一个柱子也参与运算
-
-  for (let i = 0; i < heights.length; i++) {
-    let p = i;
-
-    while (
-      ascStack.length > 0 &&
-      heights[i] < heights[ascStack[ascStack.length - 1]]
-    ) {
-      // 由于是递增栈， height[p]一定是最小的，一定是短板
-      p = ascStack.pop();
+  // const ascStack = [];
+  // let max = 0;
+  // heights.push(0); // hack, 为了使最后一个柱子也参与运算
+
+  // for (let i = 0; i < heights.length; i++) {
+  //   let p = i;
+
+  //   while (
+  //     ascStack.length > 0 &&
+  //     heights[i] < heights[ascStack[ascStack.length - 1]]
+  //   ) {
+  //     // 由于是递增栈， height[p]一定是最小的，一定是短板
+  //     p = ascStack.pop();
 
-      max = Math.max(max, heights[p] * (ascStack.length === 0 ? i : i - p));
-    }
+  //     max = Math.max(max, heights[p] * (ascStack.length === 0 ? i : i - p));
+  //   }
 
-    ascStack.push(i);
-  }
+  //   ascStack.push(i);
+  // }
 
-  return max;
+  // return max;
 
   // 相关题目： 雨水收集
 

problems/5.longest-palindromic-substring.js

@@ -0,0 +1,40 @@
+/*
+ * @lc app=leetcode id=5 lang=javascript
+ *
+ * [5] Longest Palindromic Substring
+ */
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var longestPalindrome = function(s) {
+  // babad
+  // tag : dp
+  if (!s || s.length === 0) return "";
+  let res = s[0];
+
+  const dp = [];
+  // dp[i][j] 表示 s中从i到j（包括i和j）是否可以形成回文
+
+  // 倒着遍历简化操作， 这么做的原因是dp[i][..]依赖于dp[i + 1][..]
+  for (let i = s.length - 1; i >= 0; i--) {
+    dp[i] = [];
+    for (let j = i; j < s.length; j++) {
+      if (j - i === 0) dp[i][j] = true;
+      // specail case 1
+      else if (j - i === 1 && s[i] === s[j]) dp[i][j] = true;
+      // specail case 2
+      else if (s[i] === s[j] && dp[i + 1][j - 1]) {
+        // state transition
+        dp[i][j] = true;
+      }
+
+      if (dp[i][j] && j - i + 1 > res.length) {
+        // update res
+        res = s.slice(i, j + 1);
+      }
+    }
+  }
+
+  return res;
+};

problems/516.longest-palindromic-subsequence.js

@@ -0,0 +1,29 @@
+/*
+ * @lc app=leetcode id=516 lang=javascript
+ *
+ * [516] Longest Palindromic Subsequence
+ */
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var longestPalindromeSubseq = function(s) {
+    // bbbab 返回4 
+    // tag : dp
+    const dp = [];
+
+    for(let i = s.length - 1; i >= 0; i--) {
+        dp[i] = Array(s.length).fill(0);
+        for(let j = i; j < s.length; j++) {
+            if (i - j === 0) dp[i][j] = 1;
+            else if (s[i] === s[j]) {
+                dp[i][j] = dp[i + 1][j - 1] + 2;
+            } else {
+                dp[i][j] = Math.max(dp[i][j -1], dp[i +1][j]);
+            }
+        }
+    }
+
+    return dp[0][s.length - 1]
+};
+