LeetCode 111. Minimum Depth of Binary Tree（树的最小深度）

题意：求树的最小深度。

分析：要考虑无左/右子节点的情况。

/**
 * 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;
        int leftDepth = minDepth(root -> left);
        int rightDepth = minDepth(root -> right);
        if(leftDepth == 0 || rightDepth == 0) return leftDepth + rightDepth + 1;
        return min(leftDepth, rightDepth) + 1;
    }
};