Find Largest Value in Each Tree Row宽度优先遍历算法详解

问题详见：Find Largest Value in Each Tree Row

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]

解题思路：

由题目可知该问题也是同样应用BFS算法搜索每一层以得到每一层的最大值，其算法复杂度为O(n)。下面是算法的C++代码和提交结果图。

BFS：

/**
* 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> solution;
void helper(TreeNode* node, int cl) {
if (node == NULL) {
return;
}
if (solution.size() < cl + 1) {
solution.push_back(node->val);
} else {
if (solution[cl] < node->val) {
solution[cl] = node->val;
}
}
helper(node->left, cl+1);
helper(node->right, cl+1);
}
vector<int> largestValues(TreeNode* root) {
if(root == NULL) {
return solution;
}

helper(root, 0);
return solution;
}
};

提交运行结果：