LeetCode解题报告（195）-- 111. Minimum Depth of Binary Tree

Problem

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.

Note: A leaf is a node with no children.

Example 1:

1 2	Input: root = [3,9,20,null,null,15,7] Output: 2

Example 2:

1 2	Input: root = [2,null,3,null,4,null,5,null,6] Output: 5

Constraints:

The number of nodes in the tree is in the range [0, 105].
-1000 <= Node.val <= 1000

Analysis

之前做过求二叉树最大深度的，这道题目就改为求最小深度。本质上都是通过递归调用，自下而上地增加层数，不过在每个节点处，取左右节点的最小值。

Solution

无

Code

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int minDepth(TreeNode* root) {
        if (!root) {
            return 0;
        }
        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));
    }
};

Summary

无论是算法和coding的角度，这道题都是二叉树的基本题目，之前总结果最大深度，这里也把最小深度总结一下，有头有尾，仅此而已。这道题目的分享到这里，谢谢！