最大流算法_一般曾广路算法Ford

/*
最大流增广路算法
*/
#include<iostream>
#include<queue>
#include<cstdio>
#include<cstring>
#include<cmath>
#define oo 0x3f3f3f3f
const int maxn = 1010;
using namespace std;
struct point
{
int c,f;
};
point mp[maxn][maxn];
int n,m;
int flag[maxn];
int par[maxn];
int add[maxn];
int que[maxn],qe,qs;
void Ford(int S, int T)
{
while(1)
{
memset(flag, -1,sizeof(flag));
memset(par, 0,sizeof(par));
memset(add,0,sizeof(add));
flag[S] = 0;
par[S] = 0;
add[S] = oo;
qe = qs = 0;
que[qs++] = S;
while(qe<qs&&flag[T]==-1)
{
int u = que[qe++];
for(int i = 1; i <= n; i++)
{
if(flag[i]==-1)//未标记
{
if(mp[u][i].c != oo&&mp[u][i].c-mp[u][i].f>0)//正向
{
flag[i] = 0;
par[i] = u;
add[i] = min(add[u],mp[u][i].c-mp[u][i].f);
que[qs++] = i;
}
else if(mp[i][u].c != oo && mp[i][u].f>0)//反向
{
flag[i] = 0;
par[i] = -u;
add[i] = min(add[u], mp[i][u].f);
que[qs++] = i;
}
}
}
flag[u]=1;
}

if(flag[T]==-1 || add[T]==0)break;
int k1 = T, k2 = abs(par[k1]);
int a = add[T];
while(1)
{
if(mp[k2][k1].c != oo)
{
mp[k2][k1].f += a;
}
else
mp[k1][k2].f -= a;
if(k2==S)break;
k1 = k2;
k2 = abs(par[k1]);
}
}***重点内容***
int maxFlow = 0;
for(int i = 1; i <= n; i++)
{
for(int j = 1; j <= n; j++)
{
if(i == S&&mp[i][j].f<oo)
maxFlow += mp[i][j].f;
if(mp[i][j].f<oo)
printf("%d-->%d:%d\n",i,j,mp[i][j].f);
}
}
printf("最大流：%d\n",maxFlow);
}
int main()
{
int u,v,c,f;
scanf("%d%d",&n,&m);
for(int i = 1; i <= n; i++)
{
for(int j = 1; j <= n; j++)
mp[i][j].c =  mp[i][j].f = oo;
}
for(int i = 0; i < m; i++)
{
scanf("%d%d%d%d",&u,&v,&c,&f);
mp[u][v].c = c;
mp[u][v].f = f;
}
Ford(1,n);
}
/*
6 10
1 2 4 3
1 3 8 2
2 3 4 2
2 4 4 0
2 5 1 1
3 4 2 2
3 5 2 2
4 6 7 2
5 4 6 0
5 6 9 3
6 10
1 2 8 2
1 3 4 3
2 4 2 2
2 5 2 2
3 2 4 2
3 4 1 1
3 5 4 0
4 5 6 0
4 6 9 3
5 6 7 2
*/