[Leetcode] 515. Find Largest Value in Each Tree Row 解题报告

题目：

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]

思路：

还是那句话：遇到树的问题，首先要想到DFS或者BFS。在遍历树的过程中，纪录当前结点所在的层次，然后检查该层的最大值，如果结点的值超过了该层的最大值，那么就更新。

代码：

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> largestValues(TreeNode* root) {
vector<int> ret;
largestValues(root, ret, 0);
return ret;
}
private:
void largestValues(TreeNode *root, vector<int> &ret, int height) {
if (root == NULL) {
return;
}
if (ret.size() > height) {
ret[height] = max(ret[height], root->val);
}
else {
ret.push_back(root->val);
}
largestValues(root->left, ret, height + 1);
largestValues(root->right, ret, height + 1);
}
};