leetcode 515. Find Largest Value in Each Tree Row

1.题目

找出一棵二叉树，每层节点的最大值
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]

2.分析

考察树的遍历，这里按层遍历比较直观。BFS

3.代码

class Solution {public:   vector<int> largestValues(TreeNode* root) {        vector<int> maxs;        if (root == NULL)            return maxs;        queue<pair<TreeNode*,int>> nodes;        nodes.push(pair<TreeNode*,int>(root,0));        maxs.push_back(root->val);        while (!nodes.empty()) {            root = nodes.front().first;            int level = nodes.front().second;            nodes.pop();            if (level+1 > maxs.size())                maxs.push_back(root->val);            else                maxs[level] = maxs[level] < root->val ? root->val : maxs[level];            if (root->left)                 nodes.push(pair<TreeNode*, int>(root->left, level + 1));            if (root->right)                 nodes.push(pair<TreeNode*, int>(root->right, level + 1));                   }        return maxs;    }};