【Leetcode】【Easy】Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

递归解题思路：

①结点为空时，返回0；②当前结点的深度 = max（两个孩子结点各自最大深度）+ 1

 /**
  * Definition for binary tree
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */
 class Solution {
 public:
     int maxDepth(TreeNode *root) {
         if (!root)
             return ;

         return max(maxDepth(root->left),
                 maxDepth(root->right)) + ;
     }
 };

迭代的解法：

用queue先进先出的特性，按层遍历，最后返回遍历的层数。

 class Solution {
 public:
     int maxDepth(TreeNode *root) {
         if (!root) {
             return ;
         }

         queue<TreeNode *> nodeQue;
         nodeQue.push(root);
         int levelNodesCnt;
         int depth = ;

         while (!nodeQue.empty()) {
             depth++;
             levelNodesCnt = nodeQue.size();
             while (levelNodesCnt--) {
                 if (nodeQue.front()->left)
                     nodeQue.push(nodeQue.front()->left);
                 if (nodeQue.front()->right)
                     nodeQue.push(nodeQue.front()->right);
                 nodeQue.pop();
             }
         }

         return depth;
     }
 };

附录：

C++ queue使用