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?


Example 1:
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".
Example 2:
Input:
["a"]

Output:
Return 1, and the first 1 characters of the input array should be: ["a"]

Explanation:
Nothing is replaced.
Example 3:
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.
Note:
All characters have an ASCII value in [35, 126].
1 <= len(chars) <= 1000.
'''

class Solution(object):
    def compress(self, chars):
        """
        :type chars: List[str]
        :rtype: int
        """
        ans = []
        start = 0
        end = start
        while start < len(chars):
            while end + 1 < len(chars) and chars[end + 1] == chars[start]:
                end += 1
            ans.append(chars[start])
            if end != start:
                ans += self.getStrArrayFromInt(end - start + 1)
            start = end + 1
        
        for i in xrange(len(ans)):
            chars[i] = ans[i]
        return len(ans)
    
    def getStrArrayFromInt(self, num):
        res = []
        while num > 0:
            res = [str(num % 10)] + res
            num //= 10
        return res