首頁 解題筆記 Leetcode Easy

⭐️

# 題目敘述

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

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

# Example 2

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

# 解題思路

# Solution

DFS
// Definition for a binary tree node.
public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode() {}
    TreeNode(int val) { this.val = val; }
    TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}
class Solution {
    public int minDepth(TreeNode root) {
        return dfs(root);
    }
    private int dfs(TreeNode root){
        if(root == null) return 0;
        if(root.left == null && root.right == null) return 1;
        if(root.left == null) return 1 + dfs(root.right);
        if(root.right == null) return 1 + dfs(root.left);
        return 1 + Math.min(dfs(root.left), dfs(root.right));
    }
}




單字
** **
!! !!
片語 & 搭配詞
!! !!