"""
1.3 URLify

Write a method to replace all spaces in a string with %20.
"""

def replaceSpaces(str):
    str = str.strip()
    i = len(str)
    space_count = str.count(' ')
    new_length = i + space_count * 2

    if new_length > 1000:
        return -1
    index = new_length - 1
    string = list(str)

    for f in range(i-2, new_length-2):
        string.append('0')

    for j in range(i-1,0,-1):
        if string[j] == ' ':
            string[index] = '0'
            string[index - 1] ='2'
            string[index - 2] = '%'
            index = index - 3
        else:
            string[index] = string[j]
            index -= 1
    return ''.join(string)
