POJ 1815 Friendship 最小割 + 字典序输出割点

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
#define maxn 410
#define maxm 40003
#define inf 1000000000

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

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

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(int &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;
                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 s, t;
int S, T;
int map[maxn>>1][maxn>>1], mp[maxn>>1][maxn>>1];
void build()
{
    int i, j;
    init();
    for(i = 1; i <= n; i++)
    {
        if(i == s || i == t) add(i, i+n, inf);
        else add(i, i+n, 1);
        for(j = 1; j <= n; j++)
            if(i != j && map[i][j])
                add(i+n, j, inf);
    }
}

void update(int x)
{
    int i, j;
    for(i = 1; i <= n; i++)
        for(j = 1; j <= n; j++)
            mp[i][j] = map[i][j];
    for(i = 1; i <= n; i++)
        for(j = 1; j <= n; j++)
            if( i == x || j == x)
                map[i][j] = 0;
}

void back()
{
    int i, j;
    for(i = 1; i <= n; i++)
        for(j = 1; j <= n; j++)
            map[i][j] = mp[i][j];
}
int ans[maxn>>1], num;
int main()
{
    int i, j;
    while(~scanf("%d%d%d", &n, &s, &t))
    {
        S = s; T = t + n;
        for(i = 1; i <= n; i++)
            for(j = 1; j <= n; j++)
                scanf("%d", &map[i][j]);
        if(map[s][t]) { printf("NO ANSWER!\n"); continue; }
        build();
        int f = sap(S, T, 2*n);
        printf("%d\n", f);
        num = 0;
        if(!f) continue;
        for(i = 1; i <= n; i++)
        {
            if(i == s || i == t) continue;
            update(i);
            build();
            int ff = sap(S, T, 2*n);
            if(ff < f)
            {
                f--;
                ans[num++] = i;
            }
            else 
                back();
            if(f == 0) break;
        }
        for(i = 0; i < num-1; i++)
            printf("%d ", ans[i]);
        printf("%d\n", ans[num-1]);
    }
    return 0;
}
/*
9 1 9
1 1 1 0 0 0 0 0 0
1 1 1 1 1 0 0 0 0
1 1 1 0 1 1 0 0 0
0 1 0 1 0 0 1 0 0
0 1 1 0 1 0 1 1 0
0 0 1 0 0 1 0 1 0
0 0 0 1 1 0 1 1 1
0 0 0 0 1 1 1 1 1
0 0 0 0 0 0 1 1 1

2
2 3
*/