LightOJ 1153 （网络流最大流 sap）

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
#include <queue>
#include <stack>
#include <vector>
#include <deque>
#include <set>
#include <map>
const int MAXN = 10010;//点数的最大值
const int MAXM = 10010;//边数的最大值
const int INF = 0x3f3f3f3f;
struct Edge
{
int to,next,cap,flow;
} edge[MAXM<<2]; //注意是MAXM
int tol;
int head[MAXN];
int gap[MAXN],dep[MAXN],pre[MAXN],cur[MAXN];
void init()
{
tol = 0;
memset(head,-1,sizeof (head));
}
//加边，单向图三个参数，双向图四个参数
void addedge (int u,int v,int w,int rw=0)
{
edge[tol].to = v;
edge[tol].cap = w;
edge[tol].next = head[u];
edge[tol].flow = 0;
head[u] = tol++;
edge[tol].to = u;
edge[tol].cap = w;///无向两边都流w
edge[tol]. next = head[v];
edge[tol].flow = 0;
head[v]=tol++;
}
//输入参数：起点、终点、点的总数
//点的编号没有影响，只要输入点的总数
int sap(int start,int end, int N)
{
memset(gap,0,sizeof(gap));
memset(dep,0,sizeof(dep));
memcpy(cur,head,sizeof(head));
int u = start;
pre[u] = -1;
gap[0] = N;
int ans = 0;
int i;
while(dep[start] < N)
{
if(u == end)
{
int Min = INF;
for( i = pre[u]; i != -1; i = pre[edge[i^1]. to])
{
if(Min > edge[i].cap - edge[i]. flow)
Min = edge[i].cap - edge[i].flow;
}
for( i = pre[u]; i != -1; i = pre[edge[i^1]. to])
{
edge[i].flow += Min;
edge[i^1].flow -= Min;
}
u = start;
ans += Min;
continue;
}
bool flag =  false;
int v;
for( i = cur[u]; i != -1; i = edge[i].next)
{
v = edge[i]. to;
if(edge[i].cap - edge[i].flow && dep[v]+1 == dep[u])
{
flag =  true;
cur[u] = pre[v] = i;
break;
}
}
if(flag)
{
u = v;
continue;
}
int Min = N;
for( i = head[u]; i !=  -1; i = edge[i]. next)
{
if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min)
{
Min = dep[edge[i].to];
cur[u] = i;
}
}
gap[dep[u]]--;
if(!gap[dep[u]]) return ans;
dep[u] = Min+1;
gap[dep[u]]++;
if(u != start) u = edge[pre[u]^1].to;
}
return ans;
}
int main()
{
int n,m,a,b,c,t;
int start,end;
while(~scanf("%d",&t))
{
int cas=0;
while(t--)
{
init();
scanf("%d",&n);
scanf("%d%d%d",&start,&end,&m);
for(int i=1; i<=m; i++)
{
scanf("%d%d%d",&a,&b,&c);
if(a!=b)//不建自环
addedge(a,b,c,0);
}
printf("Case %d: %d\n",++cas,sap(start,end,n));
}
}
return 0;
}