in c# public static void plusMinus(List arr) {

    int positiveNum =0  ,  negativeNum=0 ,  zeros =0;
    int size = arr.Count(); 
    foreach(int x in arr ){
        if(x >0 ){
            positiveNum++;
        }    
         else if (x<0){
             negativeNum ++;
         }
         else{
             zeros++;
         }    
    }
    Console.WriteLine((positiveNum/(double)size).ToString("F6"));
    Console.WriteLine((negativeNum/(double)size).ToString("F6"));
    Console.WriteLine((zeros/(double)size).ToString("F6"));
}

enumerate is slightly faster than for

def plusMinus(arr): positives = 0 zeros = 0 negatives = 0 size = len(arr)

for number arr:
    if number > 0 :
        positives += 1
    elif number == 0 :
        zeros += 1
    else:
        negatives += 1

print(f'{positives/size:.6f}')
print(f'{negatives/size:.6f}')
print(f'{zeros/size:.6f}')

if name == 'main': n = int(input().strip())

arr = list(map(int, input().rstrip().split()))

plusMinus(arr)

# 

public static void main(String[] args) {
   double add= 0;
    double sub=0;
    double zero=0;
    Scanner sc =new Scanner(System.in);
    // System.out.println("Enter the no of elements");
    int n =sc.nextInt();    
    int [] arr= new int[n];
    // System.out.println("Enter the elements");


    for(int i=0;i<arr.length;i++) {
        arr[i]=sc.nextInt();
        if (arr[i]>=1 && arr[i]<=100) {
            add+=1;
        }
        if (arr[i]<=-1 && arr[i]>=-100) {
            sub+=1;
        }
        if (arr[i]==0) {
            zero+=1;
        }

      }
    float n1 = n;

   System.out.printf("%.6f%n",add/n1);
   System.out.printf("%.6f%n",sub/n1);
   System.out.printf("%.6f%n",zero/n1);

    sc.close();
}

}

const { positives, negatives, zeros } = arr.reduce((acc, x) => { if (x > 0) acc.positives += 1; else if (x < 0) acc.negatives += 1; else acc.zeros += 1; return acc; }, { positives: 0, negatives: 0, zeros: 0 });

console.log((positives / length).toFixed(6));
console.log((negatives / length).toFixed(6));
console.log((zeros / length).toFixed(6));

Java streams

public static void plusMinus(List<Integer> arr) {

    long negValues = arr.stream().filter(x -> x < 0).count();
    long posValues = arr.stream().filter(x -> x > 0).count();
    long zeroValues = arr.stream().filter(x -> x == 0).count();
    long length = negValues + posValues + zeroValues;
    
    
    System.out.println((double)posValues/length);
    System.out.println((double)negValues/length);
    System.out.println((double)zeroValues/length);

    }