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Cod sursa(job #773895)
#include <cstdio>
using namespace std;
//Basic Definitions
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define MAX_NODES 1024
#define oo 1000000000
//Declarations
int n; // number of nodes
int e; // number of edges
int capacity[MAX_NODES][MAX_NODES]; // capacity matrix
int flow[MAX_NODES][MAX_NODES]; // flow matrix
int color[MAX_NODES]; // needed for breadth-first search
int pred[MAX_NODES]; // array to store augmenting path
int min (int x, int y) {
return x<y ? x : y; // returns minimum of x and y
}
//A Queue for Breadth-First Search
int head,tail;
int q[MAX_NODES+2];
void enqueue (int x) {
q[tail] = x;
tail++;
color[x] = GRAY;
}
int dequeue () {
int x = q[head];
head++;
color[x] = BLACK;
return x;
}
//Breadth-First Search for an augmenting path
int bfs (int start, int target) {
int u,v;
for (u=0; u<n; u++) {
color[u] = WHITE;
}
head = tail = 0;
enqueue(start);
pred[start] = -1;
while (head!=tail) {
u = dequeue();
// Search all adjacent white nodes v. If the capacity
// from u to v in the residual network is positive,
// enqueue v.
for (v=0; v<n; v++) {
if (color[v]==WHITE && capacity[u][v]-flow[u][v]>0) {
enqueue(v);
pred[v] = u;
}
}
}
// If the color of the target node is black now,
// it means that we reached it.
return color[target]==BLACK;
}
//Ford-Fulkerson Algorithm
int max_flow (int source, int sink) {
int i,j,u;
// Initialize empty flow.
int max_flow = 0;
for (i=0; i<n; i++) {
for (j=0; j<n; j++) {
flow[i][j] = 0;
}
}
// While there exists an augmenting path,
// increment the flow along this path.
while (bfs(source,sink)) {
// Determine the amount by which we can increment the flow.
int increment = oo;
for (u=n-1; pred[u]>=0; u=pred[u]) {
increment = min(increment,capacity[pred[u]][u]-flow[pred[u]][u]);
}
// Now increment the flow.
for (u=n-1; pred[u]>=0; u=pred[u]) {
flow[pred[u]][u] += increment;
flow[u][pred[u]] -= increment;
}
max_flow += increment;
}
// No augmenting path anymore. We are done.
return max_flow;
}
//Reading the input file and the main program
void read_input_file() {
int a,b,c,i,j;
freopen("maxflow.in","r",stdin);
// read number of nodes and edges
scanf("%d %d",&n,&e);
// initialize empty capacity matrix
for (i=0; i<n; i++) {
for (j=0; j<n; j++) {
capacity[i][j] = 0;
}
}
// read edge capacities
for (i=0; i<e; i++) {
scanf("%d %d %d",&a,&b,&c);
capacity[a-1][b-1] = c;
}
}
int main () {
read_input_file();
freopen("maxflow.out","w",stdout);
printf("%d\n",max_flow(0,n-1));
return 0;
}