public static void placeZero1(int[] arr){
        if(arr.length == 0) return;

        int start = 0, end = arr.length - 1;
        while(end >= start && arr[end] == 0) end--;
        while(start < end){
            if(arr[end] == 0){
                end--;
            }if(arr[start] != 0){
                start++;
            }else if(arr[start] == 0){
                swap(arr, start++, end--);
            }
        }
    }