zoj2587唯一最小割

从源点开始遍历，从汇点开始遍历，如果遍历了所有的点则最小割唯一，否则不唯一。

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <algorithm>

#include <cmath>

#include <stack>

#include <queue>

#include <vector>

#include <map>

#include <string>

#include <iostream>

using namespace std;

int n;int s;int e1;

const int maxn=1111;

int level[maxn];

int Min(int a,int b)

{

    return a>b?b:a;

}

const int INF=0xfffffff;

struct edge

{

  int op; int to;int next;int val;

}e[222222];



int len;int head[maxn];



void add(int from,int to,int val)

{

    e[len].to=to;e[len].val=val;e[len].next=head[from];

    e[len].op=len+1;

    head[from]=len++;

    e[len].to=from;e[len].val=0;e[len].next=head[to];

    head[to]=len++;

}



bool bfs()

{

    int q[maxn*2];int l=0;int r=0;

    memset(level,0,sizeof(level));

    level[s]=1;

    q[r++]=s;

    while(l<r){

        int cur=q[l++];

        for(int i=head[cur];i!=-1;i=e[i].next){

            int cc=e[i].to;

            if(e[i].val&&!level[cc]){

                q[r++]=cc;

                level[cc]=level[cur]+1;

            }

        }

    }

    return level[e1];

}



int dfs(int x,int val)

{

    int sum=0;if(x==e1) return val;

    for(int i=head[x];i!=-1&&val;i=e[i].next){

        int cc=e[i].to;

        if(level[cc]==level[x]+1&&e[i].val){

            int t=dfs(cc,Min(val,e[i].val));

            e[i].val-=t;e[e[i].op].val+=t;

            sum+=t;val-=t;

        }

    }

    if(sum==0) level[x]=-1;

    return sum;

}



int dinic()

{

    int ans=0;int t;

    while(bfs()){

        while(t=dfs(s,INF)) ans+=t;

    }

    return ans;

}



void judge()

{

    int vis[maxn];

    memset(vis,0,sizeof(vis));

    int q[maxn*2];int l=0;int r=0;

    q[r++]=s;

    while(l<r){

        int cur=q[l++];

        for(int i=head[cur];i!=-1;i=e[i].next){

            int cc=e[i].to;

            if(e[i].val&&!vis[cc]){

                vis[cc]=1;q[r++]=cc;

            }

        }

    }

    l=0;r=0;

    q[r++]=e1;

    while(l<r){

        int cur=q[l++];

        for(int i=head[cur];i!=-1;i=e[i].next){

            int cc=e[i].to;

            if(e[i^2].val&&!vis[cc]){

                vis[cc]=1;q[r++]=cc;

            }

        }

    }

    int ans=0;

    vis[s]=1;vis[e1]=1;

    for(int i=1;i<=n;i++)

        if(!vis[i]) ans++;

    if(!ans) printf("UNIQUE\n");

    else printf("AMBIGUOUS\n");

}

int main()

{

    int m,a,b;

    while(scanf("%d%d%d%d",&n,&m,&a,&b),n||m||a||b){

        len=0;memset(head,-1,sizeof(head));

        s=a;e1=b;

        for(int i=0;i<m;i++){

            int l;int r;int val;

            scanf("%d%d%d",&l,&r,&val);

            add(l,r,val);

            add(r,l,val);

        }

        int k=dinic();

        judge();

    }

    return 0;

}