/
O(V^2E)-Dinic.cpp
executable file
·67 lines (67 loc) · 2.01 KB
/
O(V^2E)-Dinic.cpp
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#include <bits/stdc++.h>
const int maxn = 1007, maxm = int(4e6) + 7, inf = 0x3f3f3f3f;
struct { int next, v, flow; } edge[maxm << 1];
struct Graph {
int head[maxn], cnt;
Graph() { memset(head, 0xff, sizeof(head)), cnt = 0; }
void addedge(int u, int v, int flow) {
edge[cnt] = {head[u], v, flow};
head[u] = cnt++;
edge[cnt] = {head[v], u, 0};
head[v] = cnt++;
}
} graph;
struct Dinic {
int dist[maxn], cur[maxn], que[maxn * maxn];
bool bfs(int S, int T) {
memset(dist, 0xff, sizeof(dist));
dist[S] = 0;
int head = 0, tail = 0;
que[tail++] = S;
while (head < tail) {
int u = que[head++];
for (int i = graph.head[u]; ~i; i = edge[i].next) {
int v = edge[i].v, flow = edge[i].flow;
if (dist[v] == -1 && flow > 0) {
dist[v] = dist[u] + 1;
if (v == T) return true;
que[tail++] = v;
}
}
}
return false;
}
int dfs(int u, int low, int T) {
if (u == T) return low;
for (int &i = cur[u]; ~i; i = edge[i].next) {
int v = edge[i].v, flow = edge[i].flow;
if (dist[v] == dist[u] + 1 && flow > 0) {
int min = dfs(v, flow < low ? flow : low, T);
if (min > 0) {
edge[i].flow -= min;
edge[i ^ 1].flow += min;
return min;
}
}
}
return 0;
}
int solve(int S, int T) {
int ans = 0, tmp;
while (bfs(S, T)) {
memcpy(cur, graph.head, sizeof(cur));
while (tmp = dfs(S, inf, T), tmp > 0) ans += tmp;
}
return ans;
}
} dinic;
int main() {
int n, m, s, t;
scanf("%d%d%d%d", &n, &m, &s, &t);
for (int i = 0, u, v, flow; i < m; i++) {
scanf("%d%d%d", &u, &v, &flow);
graph.addedge(u, v, flow);
}
printf("%d\n", dinic.solve(s, t));
return 0;
}