Dancing link ZOJ3209_shang[i]==1||xia[i]==1||nei[i]==1是什么意思-优快云博客

本文详细解析了DancingLinks算法的实现细节，并提供了一个具体的C++实现案例。针对常见的实现错误进行了修正说明，同时探讨了为何采用特定的数据结构。通过递归删除节点的方式解决了精确覆盖问题。

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Dancing link外面的模板其实都是错的。。看了我一天纠错，其实就是link函数的D，U，L，R（上下左右）全部弄反了，不影响结果，但是会让人无法理解。另外不明白为什么非要建个结构体？？

#include <iostream>
#include <stdio.h>
using namespace std;
int n, m, p, x1, y1, x2, y2;
int shang[101000], xia[101000], zuo[101000], you[101000], hang[101000], lie[101000];
int num[101000], hang_toujiedian[101000];
int ans, Size;
void link(int a, int b){
    num[lie[++Size] = b]++;
    shang[Size] = shang[b];
    xia[shang[b]] = Size;
    xia[Size] = b;
    shang[b] = Size;
    if(hang_toujiedian[a] < 0)
        hang_toujiedian[a] = zuo[Size] = you[Size] = Size;
    else{
        zuo[Size] = zuo[hang_toujiedian[a]];
        you[zuo[hang_toujiedian[a]]] = Size;
        you[Size] = hang_toujiedian[a];
        zuo[hang_toujiedian[a]] = Size;
    }
    return ;
}
void Remove(int a){
    zuo[you[a]] = zuo[a], you[zuo[a]] = you[a];
    for(int i = xia[a]; i != a; i = xia[i])
        for(int j = you[i]; j != i; j = you[j]){
            shang[xia[j]] = shang[j];
            xia[shang[j]] = xia[j];
            num[lie[j]]--;
        }
    return ;
}
void resume(int a){
    for(int i = shang[a]; i != a; i = shang[i])
        for(int j = zuo[i]; j != i; j = zuo[j])
            num[lie[shang[xia[j]] = xia[shang[j]] = j]]++;
    zuo[you[a]] = you[zuo[a]] = a;
    return ;
}
void Dance(int a){
    if(ans != -1 && ans <= a)
        return ;
    if(zuo[0] == 0){
        if(ans == -1 )//最简单的情况，初始情况
            ans = a;
        else if(ans > a)//如果有更小的答案更新
            ans = a;
        return ;
    }
    int c = you[0];
    for(int i = you[0]; i != 0; i = you[i])
        if(num[i] < num[c])
            c = i;
    Remove(c);
    for(int i = xia[c]; i != c; i = xia[i]){
        for(int j = zuo[i]; j != i; j = zuo[j])
            Remove(lie[j]);
        Dance(a + 1);
        for(int j = you[i]; j != i; j = you[j])
            resume(lie[j]);
    }
    resume(c);
}
int main(){
    int T;
    freopen("in.txt","r",stdin);
    cin >> T;
    while(T--){
        cin >> n >> m >> p;
        for(int i = 1; i <= n * m; i++){
            num[i] = 0;
            shang[i] = xia[i] = i;
            zuo[i + 1] = you[i - 1] = i;
        }
        zuo[0] = n * m, you[m*n] = 0, shang[0] = xia[0] = 0;
        Size = m*n;
        for(int i = 1; i <= p; i++)
            hang_toujiedian[i] = -1;
        for(int i = 1; i <= p; i++){
            cin >> x1 >> y1 >> x2 >> y2;
            for(int j = x1; j < x2; j++)
                for(int k = y1 + 1; k <= y2; k++)
                    link(i, j * m + k);
        }
        ans = -1;
        Dance(0);
        cout << ans << endl;
    }
    return 0;
}