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#include <cstddef>
struct TreeNode
{
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
#include <algorithm>
struct Result
{
// root_camera >= root_monitored >= root_not_monitored
int root_camera;
int root_monitored;
int root_not_monitored;
};
class Solution
{
public:
Result dfs(TreeNode *root)
{
if (root->left == nullptr && root->right == nullptr)
{
return Result{1, 1, 0};
}
if (root->left == nullptr || root->right == nullptr)
{
TreeNode *child_node = root->left == nullptr ? root->right : root->left;
Result child = dfs(child_node);
int root_camera = 1 + child.root_not_monitored;
int root_monitored = std::min({child.root_camera,
root_camera});
int root_not_monitored = std::min(child.root_monitored, root_monitored);
return Result{
root_camera, root_monitored, root_not_monitored};
}
Result left = dfs(root->left);
Result right = dfs(root->right);
int root_camera = 1 + left.root_not_monitored + right.root_not_monitored;
int root_monitored = std::min({left.root_camera + right.root_monitored,
left.root_monitored + right.root_camera,
root_camera});
int root_not_monitored = std::min({left.root_monitored + right.root_monitored, root_monitored});
return Result{
root_camera, root_monitored, root_not_monitored};
}
int minCameraCover(TreeNode *root)
{
auto result = dfs(root);
return result.root_monitored;
}
};
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