POJ 3740 Easy Finding

题目链接：http://poj.org/problem?id=3740

dancing links 入门题

#include <iostream>
#include <cstring>
#include <cstdio>
#include <string>
#include <iomanip>
using namespace std;
int M, N;
#define maxn 16*300+5
int R[maxn], L[maxn], U[maxn], D[maxn];
int H[maxn], C[maxn], ans[20], colsum[300+5];
int mp[18][310];
int cnt, head;
void addnode(int row, int col, int sum, int pre, int rowhead){
    cnt++;
    H[cnt] = row;  
    C[cnt] = col;
    
    if(pre == -1){ 
        R[cnt] = cnt; L[cnt] = cnt; 
    }
    else if(sum == 2){  
        R[pre] = cnt; R[cnt] = pre;
        L[pre] = cnt; L[cnt] = pre; 
    }
    else{
        R[cnt] = rowhead; R[pre] = cnt;
        L[cnt] = pre; L[rowhead] = cnt;
    }
    
    D[U[col]] = cnt;
    U[cnt] = U[col];
    D[cnt] = col;
    U[col] = cnt;
    
    colsum[col]++;
}
void init(){
        cnt = 0; head = 0;
        memset(colsum, 0, sizeof(colsum));
        L[head] = N; R[head] = 1; D[head] = head; U[head] = head;
        for(int i = 1; i <= N; i++){  
            cnt++;
            H[cnt] = 0; C[cnt] = i;
            U[cnt] = cnt; D[cnt] = cnt;
            if(i == N){
                R[cnt-1] = cnt;
                L[cnt] = cnt-1;
                R[cnt] = head;
            }
            else{
                R[cnt-1] = cnt;
                L[cnt] = cnt-1;
            } 
        }
        int temp;
        for(int i = 1; i <= M; i++){
            int sum = 0, pre = -1, rowhead;
            for(int j = 1; j <= N; j++){
                 scanf("%d", &temp);
                 if(temp == 1){
                     sum++;
                     addnode(i, j, sum, pre, rowhead);
                     if(sum == 1) rowhead = cnt;
                     pre = cnt;
                 }
            }
        }
}
void remove(int c){
    R[L[c]] = R[c];
    L[R[c]] = L[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];
            colsum[C[j]]--;
        }
    }
}
void resume(int c){
    R[L[c]] = c;
    L[R[c]] = c;
    for(int i = U[c]; i != c; i = U[i]){
        for(int j = R[i]; j != i; j = R[j]){
            U[D[j]] = j;
            D[U[j]] = j;
            colsum[C[j]]++;
        }
    }
}
bool dance(int k){
    int c = R[head];
    if(c == head){
        return true;
    }
    int min = 999999;
    for(int i = R[head]; i != head; i = R[i]){
        if(colsum[i] <= min){
            min = colsum[i];
            c = i;
        }
    }
    remove(c);
    for(int i = D[c]; i != c; i = D[i]){
        ans[k] = H[i];
        for(int j = R[i]; j != i; j = R[j]) remove(C[j]);
        if(dance(k+1)) return true;
        for(int j = L[i]; j != i; j = L[j]) resume(C[j]);
    } 
    resume(c);
    return false;    
}

int main(){
    while(~scanf("%d%d", &M, &N)){
        init();
        if(dance(0)) printf("Yes, I found it
");
        else printf("It is impossible
");
    }
    
    return 0;
}