[Leetcode] 81. 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.

解题之法

/**
 * 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 minDepth(TreeNode *root) {
        if (root == NULL) return 0;
        if (root->left == NULL && root->right == NULL) return 1;
        
        if (root->left == NULL) return minDepth(root->right) + 1;
        else if (root->right == NULL) return minDepth(root->left) + 1;
        else return 1 + min(minDepth(root->left), minDepth(root->right));
    }
    
};

分析

二叉树的经典问题之最小深度问题就是最短路径的节点个数，还是用深度优先搜索DFS来完成，万能的递归。