22 lines
820 B
C++
22 lines
820 B
C++
// 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。
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#include <bits/stdc++.h>
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using namespace std;
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int main() {
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ios::sync_with_stdio(false); cin.tie(nullptr);
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int n, m; if (!(cin >> n >> m)) return 0;
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vector<vector<bool>> reach(n, vector<bool>(n, false));
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for (int i = 0, a, b; i < m; ++i) { cin >> a >> b; reach[a-1][b-1] = true; }
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for (int k = 0; k < n; ++k) for (int i = 0; i < n; ++i) for (int j = 0; j < n; ++j)
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reach[i][j] = reach[i][j] || (reach[i][k] && reach[k][j]);
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int ans = 0;
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for (int v = 0; v < n; ++v) {
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int known = 0;
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for (int j = 0; j < n; ++j) {
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if (j == v) continue;
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if (reach[v][j] || reach[j][v]) ++known;
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}
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if (known == n-1) ++ans;
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}
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cout << ans << '\n';
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}
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