String_Compression.py

# Given an array of characters, compress it in-place.
#
# The length after compression must always be smaller than or equal to the original array.
#
# Every element of the array should be a character (not int) of length 1.
#
# After you are done modifying the input array in-place, return the new length of the array.
#
# Follow up:
# Could you solve it using only O(1) extra space?
#
# Input:
# ["a","a","b","b","c","c","c"]
#
# Output:
# Return 6, and the first 6 characters of the input array should be: ["a","2","b","2","c","3"]
#
# Explanation:
# "aa" is replaced by "a2". "bb" is replaced by "b2". "ccc" is replaced by "c3".
#
#
# Input:
# ["a"]
#
# Output:
# Return 1, and the first 1 characters of the input array should be: ["a"]
#
# Explanation:
# Nothing is replaced.
#
#
# Input:
# ["a","b","b","b","b","b","b","b","b","b","b","b","b"]
#
# Output:
# Return 4, and the first 4 characters of the input array should be: ["a","b","1","2"].
#
# Explanation:
# Since the character "a" does not repeat, it is not compressed. "bbbbbbbbbbbb" is replaced by "b12".
# Notice each digit has it's own entry in the array


class Solution:
    def compress(self, chars):
        n = len(chars)
        i = 0
        count = 1
        for j in range(1, n + 1):
            if j < n and chars[j] == chars[j - 1]:
                count += 1
            else:
                chars[i] = chars[j - 1]
                i += 1
                if count > 1:
                    for d in str(count):
                        chars[i] = d
                        i += 1
                count = 1
        return i