leetcode-java-107. Binary Tree Level Order Traversal II
阿新 • • 發佈:2019-01-29
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
/*
先層次遍歷出list
再讓list倒置
*/
public class Solution {
public List<List<Integer>> levelOrderBottom(TreeNode root) {
List <List<Integer>> list = new LinkedList<List<Integer>>();
Queue<TreeNode> queue = new LinkedList<TreeNode>();
if(root == null) {
return list;
}
queue.offer(root);
while(!queue.isEmpty()) {
int m = queue.size();
List<Integer> level = new LinkedList<Integer>();
while(m > 0) {
TreeNode node = queue.peek();
if(node.left != null) {
queue.offer(node.left);
}
if(node.right != null) {
queue.offer(node.right);
}
level.add(queue.poll().val);
m--;
}
list.add(level);
}
Collections.reverse(list);
return list;
}
}