update 4 leetcode

Author: kyriejoshua

leetcode/637.average-of-levels-in-binary-tree.js

@@ -0,0 +1,54 @@
+/*
+ * @lc app=leetcode id=637 lang=javascript
+ *
+ * [637] Average of Levels in Binary Tree
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ * this.val = (val===undefined ? 0 : val)
+ * this.left = (left===undefined ? null : left)
+ * this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[]}
+ */
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ * this.val = (val===undefined ? 0 : val)
+ * this.left = (left===undefined ? null : left)
+ * this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[]}
+ */
+var averageOfLevels = function(root) {
+ let queues = [root];
+ let level = 0;
+ let res = [];
+
+ while (queues.length) {
+ let oLen = len = queues.length;
+ let sum = 0;
+ while (len--) {
+ const cur = queues.shift() || {};
+ if (cur.val !== null) {
+ sum += cur.val;
+ }
+ cur.left && queues.push(cur.left);
+ cur.right && queues.push(cur.right);
+ }
+ res[level] = sum / oLen;
+ level++;
+ }
+
+ return res;
+};
+// @lc code=end

leetcode/783.minimum-distance-between-bst-nodes.js

@@ -0,0 +1,76 @@
+/*
+ * @lc app=leetcode id=783 lang=javascript
+ *
+ * [783] Minimum Distance Between BST Nodes
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ * this.val = (val===undefined ? 0 : val)
+ * this.left = (left===undefined ? null : left)
+ * this.right = (right===undefined ? null : right)
+ * }
+ */
+
+/**
+ * 中序遍历的方式
+ * 二叉搜索树的特性是任意两节点的差值肯定会比相邻节点的大
+ * 下面就只遍历了一次
+ * @param {*} root
+ * @returns
+ */
+var minDiffInBST = function(root) {
+ let ans = Number.MAX_SAFE_INTEGER, pre = -1;
+ const dfs = (root) => {
+ if (root === null) {
+ return;
+ }
+ dfs(root.left);
+ if (pre == -1) {
+ pre = root.val;
+ } else {
+ ans = Math.min(ans, root.val - pre);
+ pre = root.val;
+ }
+ dfs(root.right);
+ }
+ dfs(root);
+ return ans;
+};
+
+/**
+ * 遍历保存所有值，进行排序
+ * 再遍历保存差值
+ * 复杂度较高
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var minDiffInBST2 = function(root) {
+ let queues = [root];
+ let res = [];
+ let min = Number.MAX_SAFE_INTEGER;
+
+ while (queues.length) {
+ const cur = queues.shift() || {};
+ if (cur.val !== null) {
+ res.push(cur.val);
+ }
+ cur.left && queues.push(cur.left);
+ cur.right && queues.push(cur.right);
+ }
+
+ res = res.sort((a, b) => a - b);
+ res.forEach((n, index) => {
+ if (index == 0) {
+ return;
+ }
+ if (Math.abs(n - res[index - 1]) < min) {
+ min = Math.abs(n - res[index - 1]);
+ }
+ });
+
+ return min;
+};
+// @lc code=end

leetcode/876.middle-of-the-linked-list.js

@@ -0,0 +1,57 @@
+/*
+ * @lc app=leetcode id=876 lang=javascript
+ *
+ * [876] Middle of the Linked List
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ * this.val = (val===undefined ? 0 : val)
+ * this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * 快慢指针法
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var middleNode = function(head) {
+ let fast = slow = head;
+
+ // 慢的走一步，快的走两步，这样快的走到的时候，慢的正好走到一半
+ while (fast && fast.next) {
+ slow = slow.next;
+ fast = fast.next.next;
+ }
+
+ return slow;
+};
+
+/**
+ * 单指针法
+ * @param {*} head
+ * @returns
+ */
+var middleNode2 = function(head) {
+ if (!head.next) {
+ return head;
+ }
+ let h1 = h2 = head;
+ let l1 = l2 = 0;
+
+ while (h1.next) {
+ h1 = h1.next;
+ l1++;
+ }
+ const mid = ~~((l1 + 1) / 2);
+ // 这里也不一定使用循环，可以用数组保存数据，然后直接通过下标访问
+ while (l2 < mid) {
+ h2 = h2.next;
+ l2++;
+ }
+
+ return h2;
+};
+// @lc code=end

leetcode/938.range-sum-of-bst.js

@@ -0,0 +1,37 @@
+/*
+ * @lc app=leetcode id=938 lang=javascript
+ *
+ * [938] Range Sum of BST
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ * this.val = (val===undefined ? 0 : val)
+ * this.left = (left===undefined ? null : left)
+ * this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * 广度优先的遍历
+ * @param {TreeNode} root
+ * @param {number} low
+ * @param {number} high
+ * @return {number}
+ */
+var rangeSumBST = function(root, low, high) {
+ let queues = [root];
+ let sum = 0;
+
+ while (queues.length) {
+ const cur = queues.shift() || {};
+ if (cur.val <= high && cur.val >= low) {
+ sum += cur.val;
+ }
+ cur.left && queues.push(cur.left);
+ cur.right && queues.push(cur.right);
+ }
+ return sum;
+};
+// @lc code=end