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https://git.sb/baoshuo/OI-codes.git
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78 lines
1.5 KiB
C++
78 lines
1.5 KiB
C++
#include <cstring>
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#include <iostream>
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#include <limits>
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#include <queue>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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const int N = 1005,
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M = 10005;
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int n, m, s, t, ans;
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// Graph
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int idx, head[N], ver[M << 1], edge[M << 1], next[M << 1];
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void add(int u, int v, int w) {
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next[idx] = head[u];
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ver[idx] = v;
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edge[idx] = w;
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head[u] = idx++;
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}
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// Edmonds-Karp
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int d[N], pre[N];
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bool vis[N];
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bool bfs() {
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memset(vis, 0x00, sizeof(vis));
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std::queue<int> q;
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q.push(s);
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vis[s] = true;
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d[s] = std::numeric_limits<int>::max();
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while (!q.empty()) {
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int x = q.front();
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q.pop();
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for (int i = head[x]; ~i; i = next[i]) {
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if (edge[i]) {
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int y = ver[i];
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if (vis[y]) continue;
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d[y] = std::min(d[x], edge[i]);
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pre[y] = i;
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q.push(y);
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vis[y] = true;
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if (y == t) return true;
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}
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}
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}
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return false;
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}
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void update() {
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int x = t;
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while (x != s) {
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int i = pre[x];
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edge[i] -= d[t];
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edge[i ^ 1] += d[t];
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x = ver[i ^ 1];
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}
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ans += d[t];
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}
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int main() {
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std::ios::sync_with_stdio(false);
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memset(head, 0xff, sizeof(head));
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cin >> n >> m >> s >> t;
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for (int i = 1; i <= m; i++) {
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int u, v, w;
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cin >> u >> v >> w;
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add(u, v, w);
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add(v, u, 0);
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}
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while (bfs()) update();
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cout << ans << endl;
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return 0;
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}
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