public static void placeZero2(int[] arr){
        if(arr.length == 0) return;
        int count = 0;
        for(int i = 0; i < arr.length; i++){
            if(arr[i] != 0){
                arr[count++] = arr[i];
            }
        }
        while(count < arr.length) arr[count++] = 0;
    }