CC1.5 Implement a method to perform basic string compression using the counts of repeated characters. For example, the string aabcccccaaa would become a2blc5a3. If the "compressed" string would not become smaller than the original string, your method should return the original string.

StrCompression.py

# idea: traverse the string directly and count #characters. Then check whether the result is smaller than input string.
# time complexity: O(n)
# space complexity: O(n)

class Solution:
    def StrCompression(self, string):
        if string == '':
            return string

        ret = ''
        pivot = string[0]
        count = 1
        for char in string[1:]:
            if char == pivot:
                count += 1
            else:
                ret += pivot + str(count)
                pivot = char
                count = 1

        ret += pivot + str(count)
        if len(ret) < len(string):
            return ret

        return string