#864. 【2018.10雅礼集训day5】T3

https://sjzezoj.com/submission/25150

S2OJ/864/864.cpp

@@ -0,0 +1,41 @@
+#pragma GCC optimize("Ofast")
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, m, ans;
+bool f[405];
+bitset<405> g[405];
+pair<int, int> e[50005];
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin >> n >> m;
+    for (int i = 1; i <= m; i++) {
+        cin >> e[i].first >> e[i].second;
+    }
+    for (int i = 1; i <= n; i++) {
+        g[i][i] = true;
+        for (int j = m; j > 0; j--) {
+            if (g[i][e[j].first] && g[i][e[j].second]) {
+                f[i] = true;
+                break;
+            }
+            if (g[i][e[j].first] || g[i][e[j].second]) {
+                g[i][e[j].first] = g[i][e[j].second] = true;
+            }
+        }
+    }
+    for (int i = 1; i <= n; i++) {
+        if (!f[i]) {
+            for (int j = i + 1; j <= n; j++) {
+                if (!f[j] && !(g[i] & g[j]).count()) {
+                    ans++;
+                }
+            }
+        }
+    }
+    cout << ans << endl;
+    return 0;
+}