Initial commit: C++ courseware

2.Course/2.深入浅出程序设计竞赛（提高篇）/最短路/C++源码/07_11_p2419.cpp

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+// P2419 牛大赛。胜者指向败者，闭包后判断是否与其余点全部可比较。
+#include <bits/stdc++.h>
+using namespace std;
+int main() {
+    ios::sync_with_stdio(false); cin.tie(nullptr);
+    int n, m; if (!(cin >> n >> m)) return 0;
+    vector<vector<bool>> reach(n, vector<bool>(n, false));
+    for (int i = 0, a, b; i < m; ++i) { cin >> a >> b; reach[a-1][b-1] = true; }
+    for (int k = 0; k < n; ++k) for (int i = 0; i < n; ++i) for (int j = 0; j < n; ++j)
+        reach[i][j] = reach[i][j] || (reach[i][k] && reach[k][j]);
+    int ans = 0;
+    for (int v = 0; v < n; ++v) {
+        int known = 0;
+        for (int j = 0; j < n; ++j) {
+            if (j == v) continue;
+            if (reach[v][j] || reach[j][v]) ++known;
+        }
+        if (known == n-1) ++ans;
+    }
+    cout << ans << '\n';
+}