515. Find Largest Value in Each Tree Row

Problem:

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]

Analysis:

这道题是无脑用BFS。居然有人装逼用DFS,不知道怎么想的。

Solution:

class Solution {
    public List<Integer> largestValues(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        if (root == null) return res;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            int max = Integer.MIN_VALUE;
            for (int i = 0; i < size; i++) {
                TreeNode cur = queue.poll();
                max = Math.max(max, cur.val);
                if (cur.left != null) 
                    queue.offer(cur.left);
                if (cur.right != null)
                    queue.offer(cur.right);
            }
            res.add(max);
        }
        return res;
    }
}