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53 lines
1.1 KiB
53 lines
1.1 KiB
#include <iostream>
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#include <cstring>
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#include <algorithm>
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using namespace std;
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const int N = 510;
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int n, m;
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int g[N][N];
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// 匈牙利
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int match[N], st[N];
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int dfs(int u) {
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for (int i = 1; i <= n; i++)
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if (g[u][i] && !st[i]) {
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st[i] = 1;
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if (match[i] == -1 | dfs(match[i])) {
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match[i] = u;
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return 1;
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}
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}
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return 0;
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}
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int main() {
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#ifndef ONLINE_JUDGE
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freopen("POJ2594.in", "r", stdin);
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#endif
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while (scanf("%d%d", &n, &m) && (n + m)) {
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memset(g, 0, sizeof g);
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while (m--) {
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int x, y;
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scanf("%d%d", &x, &y);
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g[x][y] = 1;
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}
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// Floyd传递闭包
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for (int k = 1; k <= n; ++k)
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for (int i = 1; i <= n; ++i)
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for (int j = 1; j <= n; ++j)
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g[i][j] |= g[i][k] & g[k][j];
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int res = 0;
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memset(match, -1, sizeof match);
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for (int i = 1; i <= n; i++) {
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memset(st, 0, sizeof st);
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if (dfs(i)) res++;
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}
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printf("%d\n", n - res);
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}
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return 0;
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}
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