ISAP算法

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
#define MAXN 205
#define MAXM 1000
#define INF 0x3f3f3f3f

struct Edge {
    int v,c,next;
} e[MAXM];

int eid,NV;
int p[MAXN];

void insert(int u,int v,int c){ //插入一条从u向v，容量为c的弧。
    e[eid].v=v;
    e[eid].next=p[u];
    e[eid].c=c;
    p[u]=eid++;
}
 
void addedge(int u,int v,int c){ //用insert插入网络中的弧
    insert(u,v,c);
    insert(v,u,0);                  //插入一条反方向，当前容量为0的弧
}

int d[MAXN];
int num[MAXN];

void bfs(int vt)
{
    memset(d,-1,sizeof(d));
    memset(num,0,sizeof(num));
    d[vt]=0;
    num[d[vt]]++;
    queue<int>que;
    que.push(vt);
    while(!que.empty()) {
        int u=que.front();
        que.pop();
        for(int i=p[u]; i!=-1; i=e[i].next) {
            int v=e[i].v;
            if(d[v]!=-1)continue;
            d[v]=d[u]+1;
            num[d[v]]++;
            que.push(v);

        }
    }
}

int pre[MAXN];
int cur[MAXN];

int SAP(int s,int t)
{
    bfs(t);
    memset(pre,-1,sizeof(pre));
    memcpy(cur,p,sizeof(p));
    int u=pre[s]=s,flow=0,aug=INF;
    num[0]=NV;
    while(d[s]<NV) {
        bool flag=false;
        for(int &i=cur[u]; i!=-1; i=e[i].next) {
            int v=e[i].v;
            if(e[i].c&&d[u]==d[v]+1) {
                flag=true;
                pre[v]=u;
                u=v;
                aug=min(aug,e[i].c);
                if(v==t) {
                    flow+=aug;
                    for(u=pre[v]; v!=s; v=u,u=pre[u]) {
                        e[cur[u]].c-=aug;
                        e[cur[u]^1].c+=aug;
                    }
                    aug=INF;
                }
                break;
            }
        }
        if(flag)continue;
        int minlevel=NV;
        for(int i=p[u]; i!=-1; i=e[i].next) {
            int v=e[i].v;
            if(e[i].c&&d[v]<minlevel) {
                minlevel=d[v];
                cur[u]=i;
            }
        }
        if(--num[d[u]]==0)break;
        d[u]=minlevel+1;
        num[d[u]]++;
        u=pre[u];
    }
    return flow;
}

int main()
{
    int u,v,w,m,n,s,t;
    while(cin>>m>>n){
    	s=1,t=n,NV=n,eid=0;
	    memset(p,-1,sizeof(p));
	    while(m--){
	    	scanf("%d%d%d",&u,&v,&w);
        	addedge(u,v,w);
		}
		printf("%d\n",SAP(s,t));
	}
    return 0;
}

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
#define MAXN 205
#define MAXM 1000
#define INF 0x3f3f3f3f

struct Edge {
    int v,c,next;
} e[MAXM];

int eid,NV;
int p[MAXN];

void insert(int u,int v,int c){ //插入一条从u向v，容量为c的弧。
    e[eid].v=v;
    e[eid].next=p[u];
    e[eid].c=c;
    p[u]=eid++;
}

void addedge(int u,int v,int c){ //用insert插入网络中的弧
    insert(u,v,c);
    insert(v,u,0);                  //插入一条反方向，当前容量为0的弧
}

int gap[MAXN];
int dis[MAXN];
int cur[MAXN];
int pre[MAXN];
int rec[MAXN];
int S,T;                             //S是源点，T是汇点。

void BFS()
{
    int i;
    for(i = 0; i <= T; i++) dis[i] = INF;
    queue<int> q;
    q.push(T);
    dis[T] = 0;
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        gap[dis[u]]++;
        for(i = p[u]; i != -1; i = e[i].next)
        {
            int v = e[i].v;
            if(dis[v] == INF && e[i^1].c)
            {
                dis[v] = dis[u] + 1;
                q.push(v);
            }
        }
    }
}


int SAP()
{
    int i;
    int u = pre[S] = S, Maxflow = 0, flow = INF;

    for(i = 0; i <= T; i++)//这里 T 为最大顶点编号
    {
        gap[i] = 0;
        cur[i] = p[i];
    }
    BFS();
    while(dis[S] <= T)
    {
        if(u == T)
        {
            Maxflow += flow;
            for(; u != S; u = pre[u])
            {
                e[rec[u]].c -= flow;
                e[rec[u]^1].c += flow;
            }
            flow = INF;
        }

        for(i = cur[u]; i != -1; i = e[i].next)
        {
            int v = e[i].v;
            if(e[i].c && dis[u] == dis[v] + 1)
            {
                flow = min(flow, e[i].c);
                pre[v] = u;
                rec[v] = i;
                cur[u] = i;//当前弧优化
                u = v;
                break;
            }
        }
        if(i == -1)
        {
            int mindis = T + 1;//T是顶点数
            if((--gap[dis[u]]) == 0) break;//间隙优化
            for(i = cur[u] = p[u]; i != -1; i = e[i].next)
            {
                if(e[i].c && mindis > dis[e[i].v])
                {
                    mindis = dis[e[i].v];
                }
            }
            gap[dis[u] = mindis+1]++;
            u = pre[u];
        }
    }
    return Maxflow;
}

int main()
{
    int u,v,w,m,n;
    while(cin>>m>>n){
    	S=1,T=n,NV=n,eid=0;
	    memset(p,-1,sizeof(p));
	    while(m--){
	    	scanf("%d%d%d",&u,&v,&w);
        	addedge(u,v,w);
		}
		printf("%d\n",SAP());
	}
    return 0;
}