ZOJ 2587 Unique Attack 判最小割唯一

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
#define maxn 803
#define maxm 10003
#define inf 1000000000

int min(int a, int b)
{
    return a < b ? a : b;
}
struct E
{
    int v, next, c;
}edge[maxm<<2];

int head[maxn], tot;
int n, m, s, t;

void add(int s, int t, int c)
{
    edge[tot].v = t;
    edge[tot].c = c;
    edge[tot].next = head[s];
    head[s] = tot++;
    edge[tot].v = s;
    edge[tot].c = 0;
    edge[tot].next = head[t];
    head[t] = tot++;
}

void init()
{
    tot = 0;
    memset(head, -1, sizeof(head));
}

int gap[maxn], dis[maxn], pre[maxn], cur[maxn];

int sap(int s, int t, int vs)// s 源点，t汇点，vs顶点总数
{
    int i;
    for(i = 0; i <= vs; i++)
    {
        dis[i] = gap[i] = 0;
        cur[i] = head[i];
    }
    gap[0] = vs;
    int u = pre[s] = s, maxf = 0, aug = inf, v;
    while(dis[s] < vs)
    {
loop:   for(i = cur[u]; i != -1; i = edge[i].next)
        {
            v = edge[i].v;
            if(edge[i].c > 0 && dis[u] == dis[v] + 1)
            {
                aug = min(aug, edge[i].c);
                pre[v] = u;
                cur[u] = i;
                u = v;
                if(u == t)
                {
                    while(u != s)
                    {
                        u = pre[u];
                        edge[cur[u]].c -= aug;
                        edge[cur[u]^1].c += aug;
                    }
                    maxf += aug;
                    aug = inf;
                }
                goto loop;
            }
        }
        int min_d = vs;
        for(i = head[u]; i != -1; i = edge[i].next)
        {
            v = edge[i].v;
            if(edge[i].c > 0 && dis[v] < min_d)
            {
                min_d = dis[v];
                cur[u] = i;
            }
        }
        if( !(--gap[dis[u]])) break;
        ++gap[dis[u] = min_d + 1];
        u = pre[u];
    }
    return maxf;
}
int cnt;
bool vis[maxn];

void dfs1(int u)
{
    vis[u] =1; cnt++;
    int i, v;
    for(i = head[u]; i != -1; i = edge[i].next)
    {
        v = edge[i].v;
        if(!vis[v] && edge[i].c > 0)
            dfs1(v);
    }
}

void dfs2(int u)
{
    vis[u] = 1; cnt++;
    int i, v;
    for(i = head[u]; i != -1; i = edge[i].next)
    {
        v = edge[i].v;
        if(!vis[v] && edge[i^1].c > 0)
            dfs2(v);
    }
}
void solve()
{
    cnt = 0;
    memset(vis, 0, sizeof(vis));
    dfs1(s);
    dfs2(t);
    if(cnt == n) printf("UNIQUE\n");
    else printf("AMBIGUOUS\n");
}
int main()
{
    int i, j;
    int x, y, z;
    while( ~scanf("%d%d%d%d", &n, &m, &s, &t))
    {
        if(!n && !m && !s && !t) break;
        init();
        while(m--)
        {
            scanf("%d%d%d", &x, &y, &z);
            add(x, y, z);
            add(y, x, z);
        }
        sap(s, t, n);
        solve();
    }
    return 0;
}