LeetCode:Find Largest Value in Each Tree Row

题目链接：https://leetcode.com/problems/find-largest-value-in-each-tree-row/description/

主要思路：使用宽度优先搜索算法，遍历完一层的结点，比较得出该行的最大值，然后继续遍历下一层。

代码如下：

vector<int> largestValues(TreeNode* root) {
vector<TreeNode*> now_row;
vector<int> result;
if (root != NULL) {
now_row.push_back(root);
result.push_back(root->val);
while(!now_row.empty()) {
vector<TreeNode*> next_row;
vector<int> row_val;
while(!now_row.empty()) {
TreeNode *temp = now_row.back();
now_row.pop_back();
if (temp->left != NULL) {
row_val.push_back(temp->left->val);
next_row.push_back(temp->left);
}
if (temp->right != NULL) {
row_val.push_back(temp->right->val);
next_row.push_back(temp->right);
}
}
int max;
if (!row_val.empty()) {
max = row_val[0];
for(int i = 1; i < row_val.size(); i++) {
if (row_val[i] > max) {
max = row_val[i];
}
}
result.push_back(max);
}
now_row.clear();
for(int i = 0; i < next_row.size(); i++) {
now_row.push_back(next_row[i]);
}
}
}
return result;
}