programming-examples/c++/Basic/MaxFlowDinic.cpp

#include <algorithm>
#include <vector>
#include <climits>
#include <iostream>
using namespace std;

const int maxnodes = 5000;

int nodes = maxnodes, src, dest;
int dist[maxnodes], q[maxnodes], work[maxnodes];

struct Edge {
	int to, rev;
	int f, cap;
};

vector<Edge> g[maxnodes];

// Adds bidirectional edge
void addEdge(int s, int t, int cap){
	Edge a = {t, g[t].size(), 0, cap};
	Edge b = {s, g[s].size(), 0, cap};
	g[s].push_back(a);
	g[t].push_back(b);
}

bool dinic_bfs() {
	fill(dist, dist + nodes, -1);
	dist[src] = 0;
	int qt = 0;
	q[qt++] = src;
	for (int qh = 0; qh < qt; qh++) {
		int u = q[qh];
		for (int j = 0; j < (int) g[u].size(); j++) {
			Edge &e = g[u][j];
			int v = e.to;
			if (dist[v] < 0 && e.f < e.cap) {
				dist[v] = dist[u] + 1;
				q[qt++] = v;
			}
		}
	}
	return dist[dest] >= 0;
}

int dinic_dfs(int u, int f) {
	if (u == dest)
		return f;
	for (int &i = work[u]; i < (int) g[u].size(); i++) {
		Edge &e = g[u][i];
		if (e.cap <= e.f) continue;
		int v = e.to;
		if (dist[v] == dist[u] + 1) {
			int df = dinic_dfs(v, min(f, e.cap - e.f));
			if (df > 0) {
				e.f += df;
				g[v][e.rev].f -= df;
				return df;
			}
		}
	}
	return 0;
}

int maxFlow(int _src, int _dest) {
	src = _src;
	dest = _dest;
	int result = 0;
	while (dinic_bfs()) {
		fill(work, work + nodes, 0);
		while (int delta = dinic_dfs(src, INT_MAX))
			result += delta;
	}
	return result;
}

int main() {
    int n = 3;
    nodes = n;

    int capacity[][3] = { { 0, 3, 2 }, { 0, 0, 2 }, { 0, 0, 0 } };
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            if (capacity[i][j] != 0)
                addEdge(i, j, capacity[i][j]);
    cout << (4 == maxFlow(0, 2)) << endl;
}