add testcase

cpp/graph_util.hpp

@@ -56,7 +56,7 @@ std::vector<std::vector<int>> connected_components(const Graph<Cost>& graph) {
     std::vector<std::vector<int>> groups;
     std::vector<bool> visited(graph.n);
     for (int i = 0; i < graph.n; i++) {
-        if (color[i] != -1) continue;
+        if (visited[i]) continue;
         std::stack<int> stk;
         stk.push(i);
         visited[i] = true;

test/atcoder-abc282-d.test.cpp

@@ -0,0 +1,26 @@
+#define PROBLEM "https://atcoder.jp/contests/abc282/tasks/abc282_d"
+
+#include <array>
+
+#include "../cpp/graph_util.hpp"
+
+int main(void) {
+    int N, M;
+    std::cin >> N >> M;
+    Graph<int> graph(N);
+    graph.read(M);
+    std::vector<int> c = bipartite_coloring(graph);
+    if (c.empty()) {
+        std::cout << 0 << std::endl;
+        return 0;
+    }
+    std::vector<std::vector<int>> groups = connected_components(graph);
+    long long ans = (long long)N * (N - 1) / 2 - M;
+    for (const std::vector<int>& group : groups) {
+        std::array<long long, 2> wb = {};
+        std::for_each(group.begin(), group.end(), [&](int x) { wb[c[x]]++; });
+        auto [w, b] = wb;
+        ans -= w * (w - 1) / 2 + b * (b - 1) / 2;
+    }
+    std::cout << ans << std::endl;
+}