104. 二叉树的最大深度 about leetcode

[zzcyes]

思路

二叉树的遍历方式无非深度优先搜索和广度优先搜索两种

而实现又可分为递归和迭代

递归最简单的了，在这里遍历方式用广度优先搜索

广度优先搜索：

题解

方法一：递归

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxDepth = function(root) {
  if (root == null) {
    return 0;
  }
  let l = maxDepth(root.left);
  let r = maxDepth(root.right);
  if (root.left == null || root.right == null) {
    return l + r + 1;
  }
  return Math.max(l, r) + 1;
};

/**
 * 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 maxDepth = function(root) {
    if(root == null) return 0;
    return Math.max(maxDepth(root.left) + 1, maxDepth(root.right) + 1);
};

方法二：迭代

var maxDepth = function(root) {
    if(root == null) return 0;
    let queue = [root];
    let level = 0;
    while(queue.length) {
        let size = queue.length;
        while(size --) {
            let front = queue.shift();
            if(front.left) queue.push(front.left);
            if(front.right) queue.push(front.right);
        }
        // level ++ 后的值代表着现在已经处理完了几层节点
        level ++;
    }
    return level;
};