add: 230325

cpp/2303/230325.cpp

@@ -0,0 +1,52 @@
+#include <vector>
+#include <numeric>
+#include <unordered_map>
+#include <iostream>
+
+class UnionFindSet {
+private:
+	std::vector<int> f;
+
+public:
+	explicit UnionFindSet(int n) : f(n + 1) {
+		std::iota(f.begin(), f.end(), 0);
+	}
+
+	int find(int x) {
+		return (x == f[x]) ? x : (f[x] = find(f[x]));
+	}
+
+	// Merge y to x
+	int uni(int x, int y) {
+		return f[find(y)] = find(x);
+	}
+};
+
+/**
+ * 2316. Count Unreachable Pairs of Nodes in an Undirected Graph
+ *
+ * You are given an integer n. There is an undirected graph with n nodes, numbered from 0 to n - 1. You are given a 2D integer array edges where edges[i] = [ai, bi] denotes that there exists an undirected edge connecting nodes ai and bi.
+ * Return the number of pairs of different nodes that are unreachable from each other.
+ */
+
+class Solution {
+public:
+	static long long countPairs(int n, const std::vector<std::vector<int>>& edges) {
+		UnionFindSet ufs(n);
+		for (auto&& i : edges)
+			ufs.uni(i[0], i[1]);
+		std::unordered_map<int, int> m;
+		for (int i = 0; i < n; ++i)
+			++m[ufs.find(i)];
+		long long ret = 0;
+		for (auto&& [_, cnt] : m)
+			ret += (long long)(n - cnt) * (long long)(cnt);
+		return ret >> 1;
+	}
+};
+
+int main() {
+	std::cout << Solution::countPairs(7, {
+		{0,2},{0,5},{2,4},{1,6},{5,4}
+	});
+}

cpp/2303/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2303)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2303 230324.cpp)
+ADD_EXECUTABLE(2303 230325.cpp)