update 4 leetcode

Author: kyriejoshua

leetcode/103.binary-tree-zigzag-level-order-traversal.js

@@ -0,0 +1,51 @@
+/*
+ * @lc app=leetcode id=103 lang=javascript
+ *
+ * [103] Binary Tree Zigzag Level Order Traversal
+ */
+
+// @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)
+ * }
+ */
+/**
+ * 核心还是迭代的层序遍历
+ * @param {TreeNode} root
+ * @return {number[][]}
+ */
+var zigzagLevelOrder = function(root) {
+ let queues = [root];
+ let level = 0;
+ let ans = [];
+
+ while (queues.length) {
+ let len = queues.length;
+ // 用一个参数来标识变化
+ let isOdd = level % 2 === 0;
+
+ while (len--) {
+ let cur = queues.shift();
+ if (!cur) {
+ continue;
+ }
+ ans[level] = ans[level] || [];
+ // 根据当前奇数偶数来判断推进数组的方向
+ if (isOdd) {
+ ans[level].push(cur.val);
+ } else {
+ ans[level].unshift(cur.val);
+ }
+ queues.push(cur.left);
+ queues.push(cur.right);
+ }
+ level++;
+ }
+
+ return ans;
+};
+// @lc code=end

leetcode/107.binary-tree-level-order-traversal-ii.js

@@ -0,0 +1,44 @@
+/*
+ * @lc app=leetcode id=107 lang=javascript
+ *
+ * [107] Binary Tree Level Order Traversal II
+ */
+
+// @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
+ * @return {number[][]}
+ */
+var levelOrderBottom = function(root) {
+ let queues = [root];
+ let res = [];
+ let level = 0;
+
+ while (queues.length) {
+ let len = queues.length;
+
+ while (len--) {
+ const cur = queues.shift();
+ if (!cur) {
+ continue;
+ }
+ res[level] = res[level] || [];
+ res[level].push(cur.val);
+ queues.push(cur.left);
+ queues.push(cur.right);
+ }
+ level++;
+ }
+
+ return res.reverse();
+};
+// @lc code=end

leetcode/257.binary-tree-paths.js

@@ -0,0 +1,48 @@
+/*
+ * @lc app=leetcode id=257 lang=javascript
+ *
+ * [257] Binary Tree Paths
+ */
+
+// @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)
+ * }
+ */
+/**
+ * 深度优先遍历
+ * @param {TreeNode} root
+ * @return {string[]}
+ */
+var binaryTreePaths = function(root) {
+ let ans = []; // 用来保存结果
+ // let str = '' 不可以外部保存这样
+
+ /**
+ * 核心是把字符串作为参数传递，这样就可以保存每个节点的历史值而不至于被清空
+ * @param {*} node
+ * @param {*} str
+ */
+ function dfsWithStr(node, str = '') {
+ if (!node) {
+ return null;
+ }
+ str += node.val;
+ if (node.left === null && node.right === null) {
+ ans.push(str);
+ } else {
+ str += '->';
+ dfsWithStr(node.left, str);
+ dfsWithStr(node.right, str);
+ }
+ }
+
+ dfsWithStr(root, '');
+
+ return ans;
+};
+// @lc code=end

leetcode/513.find-bottom-left-tree-value.js

@@ -0,0 +1,43 @@
+/*
+ * @lc app=leetcode id=513 lang=javascript
+ *
+ * [513] Find Bottom Left Tree Value
+ */
+
+// @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)
+ * }
+ */
+/**
+ * 本质上还是层序遍历的思路，找到最深的一层，并返回第一个值，也就是最左侧值
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var findBottomLeftValue = function(root) {
+ let queues = [root];
+ let level = 0;
+ let ans = [];
+
+ while (queues.length) {
+ let len = queues.length;
+
+ while (len--) {
+ let cur = queues.shift();
+ if (!cur) {
+ continue;
+ }
+ ans[level] = ans[level] || [];
+ ans[level].push(cur.val);
+ cur.left && queues.push(cur.left);
+ cur.right && queues.push(cur.right);
+ }
+ level++;
+ }
+ return ans[ans.length - 1][0];
+};
+// @lc code=end