[LeetCode 111] Minimum Depth of Binary Tree

문제 바로가기

Description

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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

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

Example 2

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

Constraints

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• The number of nodes in the tree is in the range [0, 10^5].
• -1000 <= Node.val <= 1000

Code

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내 제출

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/**
 * 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) {
        if (root == null) {
            return 0;
        }
        if (root.left == null) {
            return 1 + minDepth(root.right);
        }
        if (root.right == null) {
            return 1 + minDepth(root.left);
        }
        return 1 + Math.min(minDepth(root.left), minDepth(root.right));
    }
}

Runtime	Memory
9 ms	63.3 MB

다른 풀이

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/**
 * 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) {
        //base case 
        if(root==null){
            return 0;
        }
        //if left subtree does not exist
        if(root.left==null){
            return 1+minDepth(root.right);
        }
        //if right subtree does not exist
        if(root.right==null){
            return 1+minDepth(root.left);
        }
        //if both the sub trees exist
        int leftDepth=minDepth(root.left);
        int rightDepth=minDepth(root.right);

        return 1+Math.min(leftDepth,rightDepth);
    }
}

Reference

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• https://github.com/doocs/leetcode/blob/main/solution/0100-0199/0111.Minimum%20Depth%20of%20Binary%20Tree/Solution.java