Dinic's algorithm

Author: coderick14

dinic.cpp

@@ -0,0 +1,95 @@
+#include <bits/stdc++.h>
+#define ll long long
+#define INF 1000000000000007
+using namespace std;
+
+const ll nodes = 1002;
+vector<vector<ll>> adj(nodes);
+vector<vector<ll>> capacity(nodes, vector<ll>(nodes)), flow(nodes, vector<ll>(nodes));
+vector<ll> dist, pt;
+queue<ll> q;
+ll src, dest;
+
+void add_edge(ll u, ll v, ll c) {
+	if (u != v) {
+		adj[u].push_back(v);
+		adj[v].push_back(u);
+		capacity[u][v] += c;
+		capacity[v][u] += c;
+	}
+}
+
+bool bfs(ll lim) {
+	fill(dist.begin(), dist.end(),INF);
+	dist[src] = 0;
+	q.push(src);
+
+	while (!q.empty() and dist[dest] == INF) {
+		ll u = q.front(); q.pop();
+
+		for (ll to : adj[u]) {
+			if (dist[to] == INF and capacity[u][to] - flow[u][to] >= lim) {
+				dist[to] = dist[u] + 1;
+				q.push(to);
+			}
+		}
+	}
+	while (!q.empty()) q.pop();
+
+	return dist[dest] != INF;
+}
+
+bool dfs(ll u, ll curr_flow) {
+	if (curr_flow == 0 or u == dest) {
+		return curr_flow;
+	}
+
+	for (; pt[u] < adj[u].size(); pt[u]++) {
+		ll to = adj[u][pt[u]];
+
+		if (dist[to] == dist[u] + 1 and capacity[u][to] - flow[u][to] >= curr_flow) {
+			bool pushed = dfs(to, curr_flow);
+			if (pushed) {
+				flow[u][to] += curr_flow;
+				flow[to][u] -= curr_flow;
+				return true; 
+			}
+		}
+	}
+
+	return false;
+}
+
+ll dinic() {
+	ll flow = 0, lim = (1 << 30);
+	while (lim >= 1) {
+		if (!bfs(lim)) {
+			lim >>= 1;
+			continue;
+		}
+		fill(pt.begin(), pt.end(),0);
+
+		 while (dfs(src, lim)) {
+		 	flow += lim;
+		 }
+	}
+	return flow;
+}
+
+int main() {
+	ll n,m,i,u,v,c;
+	cin >> n >> m;
+	adj.resize(n);
+	dist.resize(n);
+	pt.resize(n);
+
+	for (i = 0; i < m; i++) {
+		cin >> u >> v >> c;
+		u--;v--;
+		add_edge(u,v,c);
+	}
+	cin >> src >> dest;
+	src--;dest--;
+	cout << dinic() << endl;
+	return 0;
+}