hiho1087 Hamiltonian Cycle 位运算+记忆化搜索 求哈密顿回路数量

题目链接:

hiho1087

题目详解:

题目详解

代码:

#include<iostream>
#include<cstdio>
#include<cstring>
#define maxn 20
using namespace std;
int next_all[maxn]={0};
int pos[1<<maxn];
int dp[maxn][1<<maxn];
int n,ans=0;

int dfs(int loc,int remain)
{
    if(dp[loc][remain]!=-1)
        return dp[loc][remain];
    if(!remain)
        return dp[loc][remain]=next_all[loc]&1;

    int d=remain&next_all[loc];
    dp[loc][remain]=0;
    while(d)
    {
        int v=d&(-d);
        int remain2=remain-v;
        dp[loc][remain]+=dfs(pos[v],remain-v);
        d-=v;
    }
    return dp[loc][remain];
}

int main()
{
//    freopen("in.txt","r",stdin);
    int m,a,b;
    scanf("%d%d",&n,&m);
    memset(dp,-1,sizeof(dp));
    for(int i=0;i<n;i++)
        pos[1<<i]=i+1;
    while(m--)
    {
        scanf("%d%d",&a,&b);
        next_all[a]=next_all[a]|(1<<b-1);
    }
    dfs(1,(1<<n)-2);
    printf("%d\n",dp[1][(1<<n)-2]);
    return 0;
}