【LeetCode】Find Largest Value in Each Tree Row 解题报告

【LeetCode】Find Largest Value in Each Tree Row 解题报告

标签（空格分隔）： LeetCode

题目地址：https://leetcode.com/problems/find-largest-value-in-each-tree-row/#/description

题目描述：

You need to find the largest value in each row of a binary tree.

Example：

Input:

1
/ \
3   2
/ \   \
5   3   9

Output: [1, 3, 9]

Ways

BFS，可以背下来了。用一个队列保存每层的节点。记录下来每层的节点数目，把这个层的遍历结束，然后找出这个层的最大值。把每层的最大值保存下来，最后返回即可。

注意，level要在循环体里面初始化。

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<Integer> largestValues(TreeNode root) {
List<Integer> ans = new ArrayList<Integer>();
if(root == null){
return ans;
}
int level;
int size;
Queue<TreeNode> tree = new LinkedList<TreeNode>();
tree.offer(root);
TreeNode curr = null;
while(!tree.isEmpty()){
level = Integer.MIN_VALUE;
size = tree.size();
for(int i = 0; i < size; i++){
curr = tree.poll();
level = Math.max(level, curr.val);
if(curr.left != null){
tree.offer(curr.left);
}
if(curr.right != null){
tree.offer(curr.right);
}
}
ans.add(level);
}
return ans;
}
}

Date

2017 年 4 月 15 日