two pointers

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”]

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int compress(vector<char>& chars) {
      int ind = 0;
      int resInd = 0;
      while(ind < chars.size()){
          char curchar = chars[ind];
          int count = 0;
          while(ind < chars.size() && chars[ind] == curchar){
              ind++;
              count++;
          }
          chars[resInd++] = curchar;
          if(count > 1){
              string cs = to_string(count);
              for(int k = 0; k < cs.length(); k++)
                  chars[resInd++] = cs[k];
          }
      }

      return resInd;
  }