Sha 10160 Servicing Stations

UVA_10160

I changed this question to the Dancing Links algorithm. I did not expect the search to pass, but it took a lot of time.

Because the original Dancing Links solves the problem of precise coverage, and this problem can be overwritten repeatedly, we need to change the delete and restore operations of the Dancing Links.

Of course, there are more efficient search methods, You can google it.

#include<stdio.h>
#include<string.h>
#define INF 0x3f3f3f3f
const int MAXN = 40;
const int MAXD = MAXN * MAXN + MAXN;
int U[MAXD], D[MAXD], L[MAXD], R[MAXD], C[MAXD], H[MAXN], S[MAXN];
int vis[MAXN], del[MAXN][MAXN], N, M, Min, size, g[MAXN][MAXN];
void prepare(int r, int c)
{
int i;
for(i = 0; i <= c; i ++)
    {
        U[i] = D[i] = i;
        L[i + 1] = i, R[i] = i + 1;
        S[i] = 0;
    }
    R[c] = 0;
while(r)
        H[r --] = -1;
    size = c;
}
void insert(int r, int c)
{
    ++ size;
    C[size] = c;
    ++ S[c];
    U[size] = c;
    D[size] = D[c];
    U[D[c]] = size;
    D[c] = size;
if(H[r] == -1)
        H[r] = L[size] = R[size] = size;
else
    {
        L[size] = H[r];
        R[size] = R[H[r]];
        L[R[H[r]]] = size;
        R[H[r]] = size;
    }
}
void remove(int c)
{
    R[L[c]] = R[c];
    L[R[c]] = L[c];
}
void resume(int c)
{
    R[L[c]] = c;
    L[R[c]] = c;
}
void dance(int cur)
{
int i, j, c, min = INF;
if(!R[0])
    {
if(cur < Min)
            Min = cur;
return ;
    }
if(cur >= Min - 1)
return ;
for(i = R[0]; i != 0; i = R[i])
if(S[i] < min)
        {
            min = S[i];
            c = i;
        }
    del[cur][c] = vis[c] = 1;
    remove(c);
for(i = D[c]; i != c; i = D[i])
    {
for(j = R[i]; j != i; j = R[j])
if(!vis[C[j]])
            {
                vis[C[j]] = del[cur][C[j]] = 1;
                remove(C[j]);
            }
        dance(cur + 1);
for(j = L[i]; j != i; j = L[j])
if(del[cur][C[j]])
            {
                resume(C[j]);
                vis[C[j]] = del[cur][C[j]] = 0;
            }
    }
    resume(c);
    del[cur][c] = vis[c] = 0;
}
void solve()
{
int i, j, k, x, y;
    prepare(N, N);
    memset(g, 0, sizeof(g));
for(i = 1; i <= N; i ++)
        g[i][i] = 1;
for(i = 0; i < M; i ++)
    {
        scanf("%d%d", &x, &y);
        g[x][y] = g[y][x] = 1;
    }
for(i = 1; i <= N; i ++)
for(j = 1; j <= N; j ++)
if(g[i][j])
                insert(i, j);
    Min = INF;
    memset(del, 0, sizeof(del));
    memset(vis, 0, sizeof(vis));
    dance(0);
    printf("%d\n", Min);
}
int main()
{
for(;;)
    {
        scanf("%d%d", &N, &M);
if(!N && !M)
break;
        solve();
    }
return 0;
}