POJ 2676 Sudoku

这题数据水，可以直接暴力DFS解决

然后学了下 dancing links 就试着解决这题

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;
const int N = 9;
const int MAXN = N*N*N + 10;
const int MAXM = N*N*4 + 10;
const int M = MAXN*4 + MAXM;
char g

;
struct DLX{
int n, m, size;
int U[M], D[M], R[M], L[M], Row[M], Col[M];
int H[MAXN], S[MAXM];
int ansd, ans[MAXN];
void init(int _n,int _m){
n = _n;
m = _m;
for(int i = 0; i <= m; i++){
S[i] = 0;
U[i] = D[i] = i;
L[i] = i-1;
R[i] = i+1;
}
R[m] = 0, L[0] = m;
size = m;
for(int i = 1; i <= n; i++)H[i] = -1;
}
void Link(int r, int c){
++S[Col[++size] = c];
Row[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;
}
}
void remove(int c){
L[R[c]] = L[c]; R[L[c]] = R[c];
for(int i = D[c]; i != c; i = D[i])
for(int j = R[i];j != i;j = R[j]){
U[D[j]] = U[j];
D[U[j]] = D[j];
--S[Col[j]];
}
}
void resume(int c){
for(int i = U[c]; i != c; i = U[i])
for(int j = L[i];j != i;j = L[j])
++S[Col[U[D[j]] = D[U[j]]=j]];
L[R[c]] = R[L[c]] = c;
}
bool Dance(int d){
if(R[0] == 0){
for(int i = 0;i < d;i++)g[(ans[i]-1)/9/9][(ans[i]-1)/9%9] = (ans[i]-1)%9 + '1';
for(int i = 0 ; i < N; i++){
for(int j = 0; j < N; j++){
printf("%c",g[i][j]);
}
printf("\n");
}
return true;
}
int c = R[0];
for(int i = R[0];i != 0;i = R[i])
if(S[i] < S[c])
c = i;
remove(c);
for(int i = D[c];i != c;i = D[i]){
ans[d] = Row[i];
for(int j = R[i];j != i;j = R[j])remove(Col[j]);
if(Dance(d+1))return true;
for(int j = L[i];j != i;j = L[j])resume(Col[j]);
}
resume(c);
return false;
}
}dlx;
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;
}
int main(){
int t;
int r,c1,c2,c3,c4;
scanf("%d",&t);
while(t--){
dlx.init(N*N*N,N*N*4);
for(int i = 0 ; i < N; i++){
scanf("%s",g[i]);
for(int j = 0; j < N; j++){
for(int k = 1; k <= 9; k++){
if(g[i][j] == '0' || g[i][j] == '0'+k){
place(r,c1,c2,c3,c4,i,j,k);
dlx.Link(r,c1);
dlx.Link(r,c2);
dlx.Link(r,c3);
dlx.Link(r,c4);
}
}
}
}
dlx.Dance(0);
}
return 0;
}