POJ 3074 Sudoku

POJ_3074

I have done this question to learn how familiar I am with Dancing Links.

#include<stdio.h>
#include<string.h>
#define INF 1000000000
const int N = 9;
const int mn = N * N * N * 4 + N * N * 4 + N;
const int nn = N * N * 4 + N;
int U[mn], D[mn], L[mn], R[mn], H[mn], C[mn], X[mn];
int S[nn], Q[nn], visc[nn], size;
char b[nn];
int a[nn][nn], ans[nn][nn];
void prepare(int r, int c)
{
int i;
for(i = 0; i <= c; i ++)
    {
        S[i] = 0;
        U[i] = D[i] = i;
        L[i + 1] = i;
        R[i] = i + 1;
    }
    R[c] = 0;
    size = c;
while(r)
        H[r --] = -1;
}
void place(int &r, int &c1, int &c2, int &c3, int &c4, int i, int j, int k)
{
    r = (i * N + j) * N + k;
    c1 = i * N + j + 1;
    c2 = N * N + i * N + k;
    c3 = N * N * 2 + j * N + k;
    c4 = N * N * 3 + (i / 3 * 3 + j / 3) * N + k;
}
void link(int r , int c)
{
    size ++;
    C[size] = c;
    S[c] ++;
    X[size] = r;
    D[size] = D[c];
    U[D[c]] = size;
    U[size] = c;
    D[c] = size;
if(H[r] < 0)
        H[r] = L[size] = R[size] = size;
else
    {
        R[size] = R[H[r]];
        L[R[H[r]]] = size;
        L[size] = H[r];
        R[H[r]] = size;
    }
}
int init()
{
int i, j, k, r, c1, c2, c3, c4;
    scanf("%s", b);
if(strcmp(b, "end") == 0)
return 0;
    k = 0;
    memset(visc, 0, sizeof(visc));
    prepare(mn, N * N * 4);
for(i = 0; i < N; i ++)
for(j = 0; j < N; j ++)
        {
if(b[k] != '.')
            {
                a[i][j] = b[k] - '0';
                place(r, c1, c2, c3, c4, i, j, a[i][j]);
                link(r, c1), link(r, c2), link(r, c3), link(r, c4);
                visc[c2] = visc[c3] = visc[c4] = 1;
            }
else
             a[i][j] = 0;
            k ++;
        }
for(i = 0; i < N; i ++)
for(j = 0; j < N; j ++)
if(!a[i][j])
for(k = 1; k <= N; k ++)
                {
                    place(r, c1, c2, c3, c4, i, j, k);
if(visc[c2] || visc[c3] || visc[c4])
continue;
                    link(r, c1), link(r, c2), link(r, c3), link(r, c4);
                }
return 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;
for(i = U[c]; i != c; i = U[i])
for(j = L[i]; j != i; j = L[j])
        {
            S[C[j]] ++;
            U[D[j]] = j;
            D[U[j]] = j;
        }
    L[R[c]] = c;
    R[L[c]] = c;
}
int dance(int cur)
{
int i, j, c, temp;
if(!R[0])
    {
for(i = 0; i < cur; i ++)
        {
int x = (X[Q[i]] - 1) / N / N;
int y = (X[Q[i]] - 1) / N % N;
            ans[x][y] = (X[Q[i]] - 1) % N + 1;
        }
return 1;
    }
    temp = INF;
for(i = R[0]; i != 0; i = R[i])
if(S[i] < temp)
        {
            temp = S[i];
            c = i;
        }
    remove(c);
for(i = D[c]; i != c; i = D[i])
    {
        Q[cur] = i;
for(j = R[i]; j != i; j = R[j])
            remove(C[j]);
if(dance(cur + 1))
return 1;
for(j = L[i]; j != i; j = L[j])
            resume(C[j]);
    }
    resume(c);
return 0;
}
void printresult()
{
int i, j;
for(i = 0; i < N; i ++)
for(j = 0; j < N; j ++)
            printf("%d", ans[i][j]);
    printf("\n");
}
int main()
{
while(init())
    {
        dance(0);
        printresult();
    }
return 0;
}