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On an alien planet, every extraterrestrial is born with a number. If the sum of two numbers is a prime number, then two extraterrestrials can be friends. But every extraterrestrial can only has at most one friend. You are given all number of the extraterrestrials, please determining the maximum number of friend pair.
There are several test cases.
Each test start with positive integers N(1 ≤ N ≤ 100), which means there are N extraterrestrials on the alien planet.
The following N lines, each line contains a positive integer pi ( 2 ≤ pi
≤10^18),indicate the i-th extraterrestrial is born with pi number.
The input will finish with the end of file.
For each the case, your program will output maximum number of friend pair.
3
2
2
3
4
2
5
3
8
1 2
米勒拉宾大素数判断+二分图匹配
#include <iostream> #include <cstdio> #include <cstring> #include <cmath> using namespace std; #define N 505 typedef long long LL; LL qpow(LL a,LL b,LL r)//快速幂 { LL ans=1,buff=a; while(b) { if(b&1)ans=(ans*buff)%r; buff=(buff*buff)%r; b>>=1; } return ans; } bool Miller_Rabbin(LL n,LL a)//米勒拉宾素数测试 { LL r=0,s=n-1,j; if(!(n%a)) return false; while(!(s&1)){ s>>=1; r++; } LL k=qpow(a,s,n); if(k==1) return true; for(j=0;j<r;j++,k=k*k%n) if(k==n-1) return true; return false; } bool IsPrime(LL n)//判断是否是素数 { LL tab[]={2,3,5,7}; for(int i=0;i<4;i++) { if(n==tab[i]) return true; if(!Miller_Rabbin(n,tab[i])) return false; } return true; } int n; int graph[N][N]; int linker[N]; bool vis[N]; LL a[N]; bool dfs(int u){ for(int i=1;i<=n;i++){ if(graph[u][i]&&!vis[i]){ vis[i] = true; if(linker[i]==-1||dfs(linker[i])){ linker[i] = u; return true; } } } return false; } int main() { while(scanf("%d",&n)!=EOF){ for(int i=1;i<=n;i++){ scanf("%lld",&a[i]); } for(int i=1;i<=n;i++){ for(int j=1;j<=n;j++) graph[i][j] = 0; } for(int i=1;i<=n;i++){ for(int j=i+1;j<=n;j++){ if(IsPrime(a[i]+a[j])){ graph[i][j] = graph[j][i] = 1; } } } int ans = 0; memset(linker,-1,sizeof(linker)); for(int i=1;i<=n;i++){ memset(vis,false,sizeof(vis)); if(dfs(i)) ans++; } printf("%d\n",ans/2); } return 0; }
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原文地址：http://www.cnblogs.com/liyinggang/p/5793156.html
