ZOJ 3209 Treasure Map

ZOJ_3209

    精确覆盖问题，用Dancing Links直接求解即可。

#include<stdio.h>
#include<string.h>
#include<algorithm>
#define MAXN 510
#define MAXM 910
#define MAXD 460010
#define INF 0x3f3f3f3f
int N, M, P, size, U[MAXD], D[MAXD], L[MAXD], R[MAXD], C[MAXD];
int S[MAXM], H[MAXN], ANS, vis[MAXM];
void prep(int n, int m)
{
    int i;
    for(i = 0; i <= m; i ++)
    {
        R[i] = i + 1, L[i + 1] = i;
        U[i] = D[i] = i;
        S[i] = 0;    
    }
    R[m] = 0, size = m;
    memset(H, -1, sizeof(H[0]) * (n + 1));
}
void insert(int r, int c)
{
    ++ size;
    C[size] = c, ++ S[c];
    D[size] = D[c], U[size] = 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 init()
{
    int i, j, k, x1, x2, y1, y2;
    scanf("%d%d%d", &N, &M, &P);
    prep(P, N * M);
    for(k = 1; k <= P; k ++)
    {
        scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
        for(i = x1; i < x2; i ++)
            for(j = y1; j < y2; j ++)
                insert(k, i * M + j + 1);
    }
}
void remove(int c)
{
    int i, j;
    R[L[c]] = R[c], L[R[c]] = L[c];
    for(i = D[c]; i != c; i = D[i])
        for(j = R[i]; j != i; j = R[j])
            D[U[j]] = D[j], U[D[j]] = U[j], -- S[C[j]];
}
void resume(int c)
{
    int i, j;
    for(i = U[c]; i != c; i = U[i])
        for(j = L[i]; j != i; j = L[j])
            D[U[j]] = j, U[D[j]] = j, ++ S[C[j]];
    R[L[c]] = c, L[R[c]] = c;
}
void dance(int dep)
{
    if(R[0] == 0)
    {
        ANS = std::min(ANS, dep);
        return ;
    }
    int i, j, t = INF, id;
    for(i = R[0]; i != 0; i = R[i])
        if(S[i] < t) t = S[i], id = i;
    remove(id);
    for(i = D[id]; i != id; i = D[i])
    {
        for(j = R[i]; j != i; j = R[j]) remove(C[j]);
        dance(dep + 1);
        for(j = L[i]; j != i; j = L[j]) resume(C[j]);
    }
    resume(id);
}
void solve()
{
    ANS = INF;
    dance(0);
    printf("%d\n", ANS == INF ? -1 : ANS);
}
int main()
{
    int t;
    scanf("%d", &t);
    while(t --)
    {
        init();
        solve();
    }
    return 0;    
}