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.
题目要求二叉树的最大深度。利用递归求出最深左节点和最深右节点，然后比较取最大值，最后还要加上根节点(+1)，得到二叉树最大深度
class Solution { public: int maxDepth(TreeNode* root) { if (root == nullptr) return 0; int left = maxDepth(root->left); int right = maxDepth(root->right); return max(left, right) + 1; } }; // 6 ms
利用层次遍历在遍历每一层时引入一个计数变量，统计一共计算的层数，即可得到二叉树的最大深度。
class Solution { public: int maxDepth(TreeNode* root) { if (root == nullptr) return 0; int depth = 0; queue<TreeNode*> q; q.push(root); while (!q.empty()) { int n = q.size(); for (int i = 0; i != n; i++) { TreeNode* node = q.front(); q.pop(); if (node->left != nullptr) q.push(node->left); if (node->right != nullptr) q.push(node->right); } depth++; } return depth; } }; // 6 ms
[LeetCode] Maximum Depth of Binary Tree
原文：http://www.cnblogs.com/immjc/p/7149204.html