111.二叉树的最小深度.java

import java.util.Deque;
import java.util.LinkedList;

import javax.management.relation.Role;
import javax.swing.tree.TreeNode;

/*
 * @lc app=leetcode.cn id=111 lang=java
 *
 * [111] 二叉树的最小深度
 */

// @lc code=start
/**
 * 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;

        Deque<TreeNode> deque = new LinkedList<>();
        deque.offer(root);
        int level = 1;
        while (!deque.isEmpty()) {
            int size = deque.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = deque.poll();
                if (node.left == null && node.right == null) {
                    return level;
                } 
                // only insert node that isn't null
                if (node.left != null) {
                    deque.offer(node.left);
                } 
                if (node.right != null) {
                    deque.offer(node.right);
                }
            }
            level++;
        }
        return level;
    }
}
// @lc code=end