leetcode-day13-平衡二叉树[剑指 Offer 55

今日的题目，我之前文章有写过，前序中序后序都在这篇文章里 js实现二叉树的前序遍历，中序遍历，后续遍历

递归法

/**
 * 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 preorderTraversal = function(root) {
    let arr = [];
    (function preorderTraversalH(node){
        if(node === null) return node;
        arr.push(node.val);
        preorderTraversalH(node.left);
        preorderTraversalH(node.right);
    })(root);
    return arr;
};;

栈的方法

var preorderTraversal = function(root) {
    if(root === null) return [];
    let arr = [], stack = [];
    let node = root;
    // 先父节点再左节点再右节点，所以让右节点进栈
    while(node){
        arr.push(node.val);
        if(node.right) stack.push(node.right);
        if(node.left){
            node = node.left;
        } else {
            node = stack.pop();
        }
    }
    return arr;
}