Stoer-Wagner算法

 

论文传送门

    const int maxn = 550;
    const int inf = 1000000000;
    int n, r;
    int edge[maxn][maxn], dist[maxn];
    bool vis[maxn], bin[maxn];
    void init()
    {
        memset(edge, 0, sizeof(edge));
        memset(bin, false, sizeof(bin));
    }
    int contract( int &s, int &t )            // 寻找 s,t
    {
        memset(dist, 0, sizeof(dist));
        memset(vis, false, sizeof(vis));
        int i, j, k, mincut, maxc;
        for(i = 1; i <= n; i++)
        {
            k = -1; maxc = -1;
            for(j = 1; j <= n; j++)if(!bin[j] && !vis[j] && dist[j] > maxc)
            {
                k = j;  maxc = dist[j];
            }
            if(k == -1)return mincut;
            s = t;  t = k;
            mincut = maxc;
            vis[k] = true;
            for(j = 1; j <= n; j++)if(!bin[j] && !vis[j])
                dist[j] += edge[k][j];
        }
        return mincut;
    }
    int Stoer_Wagner()
    {
        int mincut, i, j, s, t, ans;
        for(mincut = inf, i = 1; i < n; i++)
        {
            ans = contract( s, t );
            bin[t] = true;
            if(mincut > ans)mincut = ans;
            if(mincut == 0)return 0;
            for(j = 1; j <= n; j++)if(!bin[j])
                edge[s][j] = (edge[j][s] += edge[j][t]);
        }
        return mincut;
    }