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OI-codes/AcWing/2171/2171.cpp

78 lines
1.5 KiB
C++

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