题解 | #求二叉树的层序遍历#
求二叉树的层序遍历
http://www.nowcoder.com/practice/04a5560e43e24e9db4595865dc9c63a3
import java.util.*;
/*
* public class TreeNode {
* int val = 0;
* TreeNode left = null;
* TreeNode right = null;
* }
*/
public class Solution {
/**
*
* @param root TreeNode类
* @return int整型ArrayList<ArrayList<>>
*/
public ArrayList<ArrayList<Integer>> levelOrder (TreeNode root) {
// write code here
ArrayList<ArrayList<Integer>> res = new ArrayList<>();
if (root == null) return res;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
ArrayList<Integer> tmp = new ArrayList<>();
int size = queue.size();
for (int i = 0; i < size; i++) {
TreeNode curr = queue.poll();
tmp.add(curr.val);
if (curr.left != null) queue.offer(curr.left);
if (curr.right != null) queue.offer(curr.right);
}
res.add(tmp);
}
return res;
}
}
