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[N][N];
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;
}



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