LeetCode515. Find Largest Value in Each Tree Row

一、题目

Given the root of a binary tree, return an array of the largest value in each row of the tree (0-indexed).

Example 1:

Input: root = [1,3,2,5,3,null,9]
Output: [1,3,9]
Example 2:

Input: root = [1,2,3]
Output: [1,3]

Constraints:

The number of nodes in the tree will be in the range [0, 104].
-231 <= Node.val <= 231 - 1

二、题解

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> largestValues(TreeNode* root) {
        vector<int> res;
        queue<TreeNode*> q;
        if(root != nullptr) q.push(root);
        while(!q.empty()){
            int size = q.size();
            int maxVal = q.front()->val;
            while(size--){
                TreeNode* t = q.front();
                q.pop();
                maxVal = max(maxVal,t->val);
                if(t->left != nullptr) q.push(t->left);
                if(t->right != nullptr) q.push(t->right);
            }
            res.push_back(maxVal);
        }
        return res;
    }
};