【SPOJ】1771 Yet Another NQueen Problem

#include<cstdio>
#include<cstring>
#define MAXN 1000000
#define MAXM 3000
#define INF 0x7FFFFFFF
int L[MAXN], R[MAXN], U[MAXN], D[MAXN];
int H[MAXM], S[MAXM], C[MAXN], X[MAXN], Y[MAXN], Q[MAXM], ans[MAXM], pos[MAXM];
int n, size;
bool vis[MAXM];
void Init(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 + 1;
}
inline void Link(int r, int c, int row) {
    D[size] = D[c];
    U[size] = c;
    U[D[c]] = size;
    D[c] = size;
    if (H[r] < 0)
        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;
    }
    S[c]++;
    X[size] = r;
    Y[size] = row;
    C[size++] = c;
}
void Remove(int c) {
    int i, j;
    L[R[c]] = L[c];
    R[L[c]] = R[c];
    for (i = D[c]; i != c; i = D[i]) {
        for (j = R[i]; j != i; j = R[j]) {
            U[D[j]] = U[j];
            D[U[j]] = D[j];
            S[C[j]]--;
        }
    }
}
void Resume(int c) {
    int i, j;
    R[L[c]] = L[R[c]] = c;
    for (i = D[c]; i != c; i = D[i]) {
        for (j = R[i]; j != i; j = R[j]) {
            U[D[j]] = D[U[j]] = j;
            S[C[j]]++;
        }
    }
}
bool Dance(int now) {
    int i, j, temp, c;
    if (now >= n) {
        for (i = 0; i < n; i++)
            ans[Y[pos[i]]] = Q[X[pos[i]]];
        printf("%d", ans[1]);
        for (i = 2; i <= n; i++)
            printf(" %d", ans[i]);
        putchar('\n');
        return true;
    }
    if (R[0] == 0)
        return false;
    for (temp = INF,i = R[0]; i; i = R[i]) {
        if (i > n)
            break;
        if (temp > S[i]) {
            temp = S[i];
            c = i;
        }
    }
    Remove(c);
    for (i = D[c]; i != c; i = D[i]) {
        pos[now] = i;
        for (j = R[i]; j != i; j = R[j])
            Remove(C[j]);
        if (Dance(now + 1))
            return true;
        for (j = L[i]; j != i; j = L[j])
            Resume(C[j]);
        vis[X[i]] = false;
    }
    Resume(c);
    return false;
}
void Build(int r, int c, int &k, bool flag) {
    int p1, p2, p3, p4;
    p1 = r;
    p2 = n + c;
    p3 = n + n + r + c - 1;
    p4 = 4 * n - 1 + r - c + n;
    if (flag)
        vis[p1] = vis[p2] = vis[p3] = vis[p4] = true;
    if (flag || (!vis[p1] && !vis[p2] && !vis[p3] && !vis[p4])) {
        H[++k] = -1;
        Link(k, p1, r);
        Link(k, p2, r);
        Link(k, p3, r);
        Link(k, p4, r);
        Q[k] = c;
    }
}
int main() {
    int i, j, k;
    while (~scanf("%d", &n)) {
        Init(6 * n - 2);
        memset(vis, false, sizeof(vis));
        for (k = 0, i = 1; i <= n; i++) {
            scanf("%d", &j);
            if (j)
                Build(i, j, k, true);
        }
        for (i = 1; i <= n; i++) {
            for (j = 1; j <= n; j++)
                Build(i, j, k, false);
        }
        Dance(0);
    }
    return 0;
}