二叉树先序遍历——144. Binary Tree Preorder Traversal

144. Binary Tree Preorder Traversal

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

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/** * https://leetcode.com/problems/binary-tree-preorder-traversal/#/description *  * Definition for a binary tree node. * function TreeNode(val) { *     this.val = val; *     this.left = this.right = null; * } *//** * @param {TreeNode} root * @return {number[]} *//** * 先序遍历非递归 * 1.申请一个stack,如果根节点存在，将根节点push到stack中 * 2.从stackpop一个节点，执行操作后，如果右边还是存在push到stack中，如果左边还是存在push到stack中 * 3.重复2直到stack为空 */    var preorderTraversal = function(root) {        var stack = [],            node,            result = [];        if (!root) return result;        stack.push(root);        while (stack.length) {            node = stack.pop();            result.push(node.val);            if (node.right) stack.push(node.right);            if (node.left) stack.push(node.left);        }        return result;    };