443.md

443. String Compression

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.

my thoughts:

1. The problem is not clear with [aaaabbbbaacccddddddaaaaaaaa] case
my guess is that only the contiguous repeating char can be compressed. so still a two pointer solution:
l,r = 0,1, count = 0; go right, if l=r, r+=1, count+=1 else (if count > 0, count to chars ) l=r, r+=1, count = 0

my solution:

**********72ms
class Solution(object):
    def compress(self, chars):
        """
        :type chars: List[str]
        :rtype: int
        """
        if len(chars) == 1: return 1
        length = len(chars)
        l = 0
        r = 1
        c = 1
        gc = 0
        while r<length:
            if chars[l]==chars[r]:
                c += 1
                
            else:
                if c > 1:
                    chars[gc] = chars[l]
                    gc += 1
                    for char in str(c):
                        chars[gc] = char
                        gc += 1
                    
                    c = 1
                else:
                    chars[gc] = chars[l]
                    gc += 1
                l = r                
            r += 1    
        chars[gc] = chars[l]
        gc += 1
        if c>1:
            for char in str(c):
                chars[gc] = char
                gc += 1      
            
        return gc
        
        
            
        

my comments:

need to better understand that the function can do one thing (mutate the chars arr) and return other thing (the length of the compressed arr)
from other ppl's solution:

1. N/A