UVA - 524 Prime Ring Problem

#include<bits/stdc++.h>
using namespace std;

typedef pair<int,int>Pair;

int n;

bool is_prime(int x)
{
    for(int i = 2; i <= sqrt(x); i++){
        if(x % i == 0){
            return false;
        }
    }
    return true;
}
void solve(int cur, int* A)
{
    if(cur == n){
        if(is_prime(A[0] + A[cur-1])){
            cout << A[0];
            for(int i = 1; i < n; i++)
                cout << " " << A[i];
            cout << endl;
        }
    }else{
        for(int i = 1; i <= n; i++){
            if(is_prime(A[cur-1] + i)){ //符合质数条件 并且 此数尚未用
                int ok = true;
                for(int j = 0; j < cur; j++){
                    if(A[j] == i){
                        ok = false;
                        break;
                    }
                }
                if(ok){
                    A[cur] = i;
                    solve(cur + 1, A);
                }
            }

        }
    }
}

int main()
{
//    freopen("in.txt", "r", stdin);
//    freopen("out.txt", "w", stdout);
    int kase= 0;
    bool first = true;
    while(cin >> n){
        if(first){
            first = false;
        }else
            cout << endl;
        printf("Case %d:\n", ++kase);
        int A[n] = {1};
        solve(1, A);
    }
    return 0;
}