mirror of
https://git.sb/baoshuo/OI-codes.git
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134 lines
2.5 KiB
C++
134 lines
2.5 KiB
C++
#include <iostream>
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#include <cstring>
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#include <fstream>
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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 = 5e4 + 5,
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M = 125003 + 5;
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int n, m, s, t, ss, tt;
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int idx, head[N], ver[M << 2], edge[M << 2], next[M << 2];
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int f[N], cur[N], dist[N];
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void add(int u, int v, int w) {
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ver[idx] = v;
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edge[idx] = w;
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next[idx] = head[u];
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head[u] = idx++;
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}
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bool bfs() {
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memset(dist, 0x00, sizeof(dist));
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std::queue<int> q;
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q.push(s);
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dist[s] = 1;
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cur[s] = head[s];
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while (!q.empty()) {
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int u = q.front();
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q.pop();
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for (int i = head[u]; ~i; i = next[i]) {
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int v = ver[i],
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w = edge[i];
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if (!dist[v] && w) {
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dist[v] = dist[u] + 1;
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cur[v] = head[v];
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if (v == t) return true;
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q.push(v);
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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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int dinic(int u, int limit) {
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if (u == t) return limit;
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int flow = 0;
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for (int i = cur[u]; ~i && flow < limit; i = next[i]) {
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cur[u] = i;
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int v = ver[i],
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w = edge[i];
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if (dist[v] == dist[u] + 1 && w) {
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int k = dinic(v, std::min(w, limit - flow));
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if (!k) dist[v] = 0;
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edge[i] -= k;
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edge[i ^ 1] += k;
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flow += k;
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}
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}
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return flow;
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}
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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memset(head, 0xff, sizeof(head));
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cin >> n >> m >> ss >> tt;
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for (int i = 1, u, v, a, b; i <= m; i++) {
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cin >> u >> v >> a >> b;
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add(u, v, b - a);
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add(v, u, 0);
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f[u] -= a, f[v] += a;
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}
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int sum = 0;
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s = 0, t = n + 1;
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for (int i = 1; i <= n; i++) {
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if (f[i] > 0) {
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add(s, i, f[i]);
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add(i, s, 0);
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sum += f[i];
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} else if (f[i] < 0) {
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add(i, t, -f[i]);
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add(t, i, 0);
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}
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}
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add(tt, ss, std::numeric_limits<int>::max());
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add(ss, tt, 0);
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int res = 0, flow;
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while (bfs()) {
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while (flow = dinic(s, std::numeric_limits<int>::max())) res += flow;
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}
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if (res == sum) {
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int x = edge[idx - 1];
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edge[idx - 1] = edge[idx - 2] = 0;
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s = tt, t = ss;
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int res = 0, flow;
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while (bfs()) {
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while (flow = dinic(s, std::numeric_limits<int>::max())) res += flow;
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}
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cout << x - res << endl;
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} else {
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cout << "No Solution" << endl;
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}
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return 0;
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}
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