【题目描述】
A Sudoku grid is a 16x16 grid of cells grouped in sixteen 4x4 squares, where some cells are filled with letters from A to P (the first 16 capital letters of the English alphabet), as shown in figure 1a. The game is to fill all the empty grid cells with letters from A to P such that each letter from the grid occurs once only in the line, the column, and the 4x4 square it occupies. The initial content of the grid satisfies the constraints mentioned above and guarantees a unique solution.

Write a Sudoku playing program that reads data sets from a text file. Each data set encodes a grid and contains 16 strings on 16 consecutive lines as shown in figure 2. The i th string stands for the i th line of the grid, is 16 characters long, and starts from the first position of the line. String characters are from the set {A,B,…,P,-}, where - (minus) designates empty grid cells. The data sets are separated by single empty lines and terminate with an end of file. The program prints the solution of the input encoded grids in the same format and order as used for input.

【样例输入】
–A----C-----O-I
-J–A-B-P-CGF-H-
–D--F-I-E----P-
-G-EL-H----M-J–
----E----C–G—
-I–K-GA-B—E-J
D-GP–J-F----A–
-E—C-B–DP–OE–
F-M–D--L-K-A
-C--------O-I-LH-
P-C–F-A–B—
—G-OD—J----H
K—J----H-A-P-L
–B--P–E--K–A-
-H–B--K–FI-C–
–F—C–D--H-N-
上面题面给的样例是错的
正确的样例是这个
–A----C-----O-I
-J–A-B-P-CGF-H-
–D--F-I-E----P-
-G-EL-H----M-J–
----E----C–G—
-I–K-GA-B—E-J
D-GP–J-F----A–
-E—C-B–DP–O-
E–F-M–D--L-K-A
-C--------O-I-L-
H-P-C–F-A–B—
—G-OD—J----H
K—J----H-A-P-L
–B--P–E--K–A-
-H–B--K–FI-C–
–F—C–D--H-N-

【样例输出】
FPAHMJECNLBDKOGI
OJMIANBDPKCGFLHE
LNDKGFOIJEAHMBPC
BGCELKHPOFIMAJDN
MFHBELPOACKJGNID
CILNKDGAHBMOPEFJ
DOGPIHJMFNLECAKB
JEKAFCNBGIDPLHOM
EBOFPMIJDGHLNKCA
NCJDHBAEKMOFIGLP
HMPLCGKFIAENBDJO
AKIGNODLBPJCEFMH
KDEMJIFNCHGAOPBL
GLBCDPMHEONKJIAF
PHNOBALKMJFIDCEG
IAFJOECGLDPBHMNK

题目链接：https://cn.vjudge.net/problem/ZOJ-3122

POJ1084的升级版，但是其实没什么区别

代码如下：

#include <iostream>
using namespace std;
static const int MAXN=16*16*16+10;
static const int MAXM=16*16*4+10;
static const int MAXNODE=MAXN*4+MAXM+10;
char g[MAXN];
struct DLX{
    int n,m,size;
    int U[MAXNODE],D[MAXNODE],L[MAXNODE],R[MAXNODE],Row[MAXNODE],Col[MAXNODE];
    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)/16]=(ans[i]-1)%16+'A';
            for(int i=0;i<16;i++)
            {
                for(int j=0;j<16;j++)
                    cout<<g[i*16+j];
                cout<<endl;
            }
            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;
    }
};
int main()
{
    std::ios::sync_with_stdio(false);
    std::cin.tie(0),cout.tie(0);
    int kase=0;
    while(cin>>g)
    {
        if(kase)
            cout<<endl;
        kase++;
        for(int i=1;i<=15;i++)
            cin>>g+i*16;
        DLX dlx;
        dlx.init(16*16*16,16*16*4);
        for(int i=0;i<16;i++)
            for(int j=0;j<16;j++)
                for(int k=1;k<=16;k++)
                    if(g[i*16+j]=='-' || g[i*16+j]=='A'+k-1)
                    {
                        dlx.Link((i*16+j)*16+k,i*16+j+1);
                        dlx.Link((i*16+j)*16+k,16*16+i*16+k);
                        dlx.Link((i*16+j)*16+k,16*16*2+j*16+k);
                        dlx.Link((i*16+j)*16+k,16*16*3+((i/4)*4+(j/4))*16+k);
                    }
        dlx.dance(0);
    }
    return 0;
}