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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:

  1. All characters have an ASCII value in [35, 126].
  2. 1 <= len(chars) <= 1000.

Solutions (Python)

1. Two Pointers

classSolution: defcompress(self, chars: List[str]) ->int: r, w_char, w_pos=0, 0, 0forrinrange(len(chars)): ifr==len(chars) -1orchars[r] !=chars[r+1]: s=chars[w_char] + (str(r-w_char+1) ifr>w_charelse"") forchins: chars[w_pos] =chw_pos+=1w_char=r+1returnw_pos
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