【HDU】3909 Sudoku

#include<cstdio>
#include<cstring>
#define SD 16
#define MAXN 2400000
#define MAXM 4100
#define INF 0x7FFFFFFF
char sd[SD][SD];
int L[MAXN], R[MAXN], U[MAXN], D[MAXN], C[MAXN], X[MAXN];
int size, cnt, row, S[MAXM], H[MAXM], Q[MAXM], ans[MAXM];
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;
}
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;
    L[R[c]] = c;
    R[L[c]] = c;
    for (i = D[c]; i != c; i = D[i])
    {
        for (j = R[i]; j != i; j = R[j])
        {
            U[D[j]] = j;
            D[U[j]] = j;
            S[C[j]]++;
        }
    }
}
inline void Link(int r, int c)
{
    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;
    C[size++] = c;
}
void Build(int n)
{
    int i, j, k, t;
    Init(n * n << 2);
    if (n == 4)
        t = 2;
    else if (n == 9)
        t = 3;
    else
        t = 4;
    for (i = row = 0; i < n; i++)
    {
        for (j = 0; j < n; j++)
        {
            if (sd[i][j] == '.')
            {
                for (k = 0; k < n; k++)
                {
                    H[++row] = -1;
                    Q[row] = k;
                    Link(row, i * n + k + 1);
                    Link(row, n * n + j * n + k + 1);
                    Link(row, (n * n << 1) + (i / t * t + j / t) * n + k + 1);
                    Link(row, n * n * 3 + i * n + j + 1);
                }
            }
            else
            {
                if (sd[i][j] >= '0' && sd[i][j] <= '9')
                    k = sd[i][j] - '1';
                else
                    k = sd[i][j] - 'A' + 9;
                H[++row] = -1;
                Q[row] = k;
                Link(row, i * n + k + 1);
                Link(row, n * n + j * n + k + 1);
                Link(row, (n * n << 1) + (i / t * t + j / t) * n + k + 1);
                Link(row, n * n * 3 + i * n + j + 1);
            }
        }
    }
}
bool Dance(bool flag)
{
    int i, j, temp, c;
    if (R[0] == 0)
    {
        if (flag && !cnt)
        {
            for (i = j = 1; i <= row; i++)
            {
                if (vis[i])
                    ans[j++] = Q[i];
            }
        }
        cnt++;
        return cnt > 1;
    }
    for (temp = INF,i = R[0]; i; i = R[i])
    {
        if (temp > S[i])
        {
            temp = S[i];
            c = i;
        }
    }
    Remove(c);
    for (i = D[c]; i != c; i = D[i])
    {
        vis[X[i]] = true;
        for (j = R[i]; j != i; j = R[j])
            Remove(C[j]);
        if (Dance(flag))
            return true;
        for (j = L[i]; j != i; j = L[j])
            Resume(C[j]);
        vis[X[i]] = false;
    }
    Resume(c);
    return false;
}
bool OK(int n)
{
    int i, j;
    char temp;
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < n; j++)
        {
            if (sd[i][j] != '.')
            {
                temp = sd[i][j];
                sd[i][j] = '.';
                Build(n);
                cnt = 0;
                Dance(false);
                if (cnt < 2)
                    return false;
                sd[i][j] = temp;
            }
        }
    }
    return true;
}
int main()
{
    int n, i, j;
    while (~scanf("%d", &n))
    {
        n *= n;
        for (cnt = i = 0; i < n; i++)
        {
            for (j = 0; j < n; j++)
                scanf(" %c", &sd[i][j]);
        }
        memset(vis, false, sizeof(vis));
        Build(n);
        Dance(true);
        if (cnt == 0)
            puts("No Solution");
        else if (cnt > 1)
            puts("Multiple Solutions");
        else
        {
            if (OK(n))
            {
                for (i = 1; i <= n * n; i++)
                {
                    if (ans[i] < 9)
                        putchar(ans[i] + 1 + '0');
                    else
                        putchar(ans[i] - 9 + 'A');
                    if (i % n == 0)
                        putchar('\n');
                }
            }
            else
                puts("Not Minimal");
        }
    }
    return 0;
}