111. Minimum Depth of Binary Tree

/**
 * 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) return 0;
        //注意是leaves 所以需要下面两个if检查是不是叶子节点
        if(!root->left) return 1+minDepth(root->right);
        if(!root->right) return 1+minDepth(root->left);
        return 1+min(minDepth(root->left),minDepth(root->right));
    }
};