968

/**
 * 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 {
public:
    int ans=0;
    int dfs(TreeNode* curr){
        // 2 -> grandparent
        // 1 -> parent
        // 0 -> child/leaf
        // Place camera only at parent  node only.

        if(!curr) return 2;
        int left = dfs(curr->left);
        int right = dfs(curr->right);
        if(left == 0 || right == 0){
            ans++;
            return 1;
        }
        if(left == 1 || right == 1)
            return 2;
        return 0;
    }

    int minCameraCover(TreeNode* root) {
        if(dfs(root) == 0) ans++;
        return ans;
    }
};