题解 | #求二叉树的层序遍历#队列实现
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) {
ArrayList<ArrayList<Integer>> res = new ArrayList<>();
ArrayList<Integer> al = null;
LinkedList<TreeNode> queue = new LinkedList<>();
if( root == null ) return res;
queue.add(root);
while( !queue.isEmpty()){
al = new ArrayList<>();
int size = queue.size();
for(int i=0;i<size;i++){
TreeNode node = queue.removeFirst();
al.add(node.val);
if( node.left != null ){
queue.add(node.left);
}
if( node.right != null ){
queue.add(node.right);
}
}
res.add(al);
}
return res;
}
} 