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OI-codes/AcWing/2190/2190.cpp

134 lines
2.5 KiB
C++

#include <iostream>
#include <cstring>
#include <fstream>
#include <limits>
#include <queue>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 5e4 + 5,
M = 125003 + 5;
int n, m, s, t, ss, tt;
int idx, head[N], ver[M << 2], edge[M << 2], next[M << 2];
int f[N], cur[N], dist[N];
void add(int u, int v, int w) {
ver[idx] = v;
edge[idx] = w;
next[idx] = head[u];
head[u] = idx++;
}
bool bfs() {
memset(dist, 0x00, sizeof(dist));
std::queue<int> q;
q.push(s);
dist[s] = 1;
cur[s] = head[s];
while (!q.empty()) {
int u = q.front();
q.pop();
for (int i = head[u]; ~i; i = next[i]) {
int v = ver[i],
w = edge[i];
if (!dist[v] && w) {
dist[v] = dist[u] + 1;
cur[v] = head[v];
if (v == t) return true;
q.push(v);
}
}
}
return false;
}
int dinic(int u, int limit) {
if (u == t) return limit;
int flow = 0;
for (int i = cur[u]; ~i && flow < limit; i = next[i]) {
cur[u] = i;
int v = ver[i],
w = edge[i];
if (dist[v] == dist[u] + 1 && w) {
int k = dinic(v, std::min(w, limit - flow));
if (!k) dist[v] = 0;
edge[i] -= k;
edge[i ^ 1] += k;
flow += k;
}
}
return flow;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
memset(head, 0xff, sizeof(head));
cin >> n >> m >> ss >> tt;
for (int i = 1, u, v, a, b; i <= m; i++) {
cin >> u >> v >> a >> b;
add(u, v, b - a);
add(v, u, 0);
f[u] -= a, f[v] += a;
}
int sum = 0;
s = 0, t = n + 1;
for (int i = 1; i <= n; i++) {
if (f[i] > 0) {
add(s, i, f[i]);
add(i, s, 0);
sum += f[i];
} else if (f[i] < 0) {
add(i, t, -f[i]);
add(t, i, 0);
}
}
add(tt, ss, std::numeric_limits<int>::max());
add(ss, tt, 0);
int res = 0, flow;
while (bfs()) {
while (flow = dinic(s, std::numeric_limits<int>::max())) res += flow;
}
if (res == sum) {
int x = edge[idx - 1];
edge[idx - 1] = edge[idx - 2] = 0;
s = tt, t = ss;
int res = 0, flow;
while (bfs()) {
while (flow = dinic(s, std::numeric_limits<int>::max())) res += flow;
}
cout << x - res << endl;
} else {
cout << "No Solution" << endl;
}
return 0;
}