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 {
public:
    int compress(vector<char>& chars) {
        int start=1;
        int count=1;
        int res=0;
        for(int i=1;i<chars.size();i++)
        {
            if(chars[i]==chars[i-1])
                count++;
            else
            {
                if(count==1){
                    res+=1;
                }
                else
                {
                    string tmp=to_string(count);
                    res+=1+tmp.length();
                    for(auto c:tmp)
                        chars[start++]=c;         
                    count=1;
​
                 }
                chars[start++]=chars[i];
            }                  
        }
​
         if(count==1){
                    res+=1;
                }
                else
                {
                    string tmp=to_string(count);
                    res+=1+tmp.length();
                    for(auto c:tmp)
                        chars[start++]=c;         
                 }
            return res;
    }
};