
def add_one(arr):
    '''
    input : list represent the number
    output : list represent the number plus 1
    '''
    output = 1;

    for i in range(len(arr), 0, -1):
        output = output + arr[i - 1]
        borrow = output//10
        if borrow == 0:
            arr[i - 1] = output
            break
        else:
            arr[i - 1] = output % 10
            output = borrow
    arr = [borrow] + arr
    index = 0
    while arr[index]==0:
        index += 1
    return arr[index:]