【LeetCode从零单刷】Minimum Depth of Binary Tree

题目：

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

解答：

非常无聊的一题。需要注意的是：叶子节点是自身不为 NULL，但是左子树与右子树同时为 NULL 的节点。

所以，只要左右子树任意一棵不为 NULL，寻找 depth 的过程就不能停止。

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:        int minDepth(TreeNode* root) {        if (root == NULL)   return 0;        if (root->left == NULL && root->right != NULL)  return minDepth(root->right) + 1;        if (root->right == NULL && root->left != NULL)  return minDepth(root->left) + 1;        return min( minDepth(root->left), minDepth(root->right) ) + 1;    }};