[Level 1] 소수 만들기

class Solution {
    public int answer = 0;
    public boolean[] visit;
    
    public int solution(int[] nums) {
        visit = new boolean[nums.length];
        
        recur(0, 0, nums, 0);
        
        return answer;
    }
    
    public void recur(int count, int start, int[] nums, int sum) {
        if(count==3) {
            if(isPrime(sum)) { answer++; }
            return;
        }
        
        for(int i=start; i<nums.length; i++) {
            if(visit[i]) { continue; }
            
            visit[i] = true;
            recur(count+1, i+1, nums, sum+nums[i]);
            visit[i] = false;
        }
    }
    
    public boolean isPrime(int n) {
        if(n==1) { return false; }
        
        for(int i=2; i*i<=n; i++) {
            if(n%i==0) { return false; }
        }
        
        return true;
    }
}