题解 | #素数伴侣#

#include <stdio.h>
#include <math.h>
#include <string.h>

int isp[60005];
int n,a[105],book[105],match[105];

void su(){
    isp[0]=isp[1]=1;
    for(int i=2;i<=60000;i++)
        if(isp[i]==0){
            for(int j=2*i;j<=60000;j+=i) isp[j]=1;
        }
}

int dfs(int x){
    for(int i=0;i<n;i++){
        if(a[i]%2!=0&&isp[a[i]+a[x]]==0&&book[i]==0){
            book[i]=1;
            if(match[i]==-1||dfs(match[i])){
                //printf("%d->%d\n",a[x],a[i]);
                match[i]=x;
                match[x]=i;
                return 1;
            }
        }
    }
    return 0;
}

int main() {
    int count=0;
    memset(isp,0,sizeof(isp));
    su();
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        scanf("%d",&a[i]);
    }
    memset(match,-1,sizeof(match));
    for(int i=0;i<n;i++){
        if(a[i]%2==0){
            memset(book,0,sizeof(book));
            book[i]=1;
            if(dfs(i)){
                count++;
            }
        }
    }
    printf("%d",count);
    return 0;
}