968. Binary Tree Cameras
Đề Bài
You are given the root of a binary tree. We install cameras on the tree nodes where each camera at a node can monitor its parent, itself, and its immediate children.
Return the minimum number of cameras needed to monitor all nodes of the tree.
Example 1:
Input: root = [0,0,null,0,0] Output: 1 Explanation: One camera is enough to monitor all nodes if placed as shown.
Example 2:
Input: root = [0,0,null,0,null,0,null,null,0] Output: 2 Explanation: At least two cameras are needed to monitor all nodes of the tree. The above image shows one of the valid configurations of camera placement.
Constraints:
- The number of nodes in the tree is in the range
[1, 1000]. Node.val == 0
Thuật Toán & Kỹ Thuật
⏱️ Thời gian
O(V+E)
💾 Không gian
O(V)
Lời Giải
C++
0968-binary-tree-cameras.cpp
/**
* 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 {
private:
int res = 0;
public:
int dfs(TreeNode* root) {
if (!root) {
return 1;
}
int node_left = dfs(root->left);
int node_right = dfs(root->right);
if (node_left == 0 or node_right == 0) {
res++;
return 2;
}
if (node_left == 2 or node_right == 2) {
return 1;
}
return 0;
}
int minCameraCover(TreeNode* root) {
if (dfs(root) == 0) {
res++;
}
return res;
}
};