#leetcode#515. Find Largest Element in Each Row

515. Find Largest Element in Each Row

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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]

Discuss

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还是一道BFS的题，每层记录一下当前层的最大值即可，值得注意的是这里当input为null时要求返回的是一个空的array，当然实际面试时返回null也不无不可

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int[] findValueMostElement(TreeNode root) {
        if(root == null)    return new int[0];
        List list = new ArrayList<>();
        LinkedList queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int tmpMax = Integer.MIN_VALUE;
            int size = queue.size();
            for(int i = 0; i < size; i++){
                TreeNode cur = queue.poll();
                tmpMax = Math.max(tmpMax, cur.val);
                if(cur.left != null)    queue.offer(cur.left);
                if(cur.right != null)   queue.offer(cur.right);
            }
            list.add(tmpMax);
        }
        int[] res = new int[list.size()];
        for(int j = 0; j < list.size(); j++){
            res[j] = list.get(j);
        }
        
        return res;
    }
}