public class Permutation {
    public static int JOKER = 0;

    public static boolean isPermutation(int[] a) {
        int l=a.length;
        for(int i=0; i<l;i++) {
            boolean[] f = new boolean[l+1];
            int n=a[i];
            if(n==JOKER) continue;
            if(n < 1 || n > l) return false;
            if(f[n]) return false;
            f[n]=true;
        }
        return true;
    }

    public static void main(String[] args) {
        System.out.println(isPermutation(new int[] {1,1,1,4}));
    }

}