zoj2587唯一最小割

#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;
}