821. Shortest Distance to a Character

 class Solution
 {
 public:
     vector<int> shortestToChar(string S, char C)
     {
         int len=S.length();
         vector<int>res(len,-);                   //as the result vector
         vector<int> cindex;                       //save the index of C
         for(int i=;i<len;i++)                    //write the distance of C and build the cindex
             if(S[i]==C)
             {
                 cindex.push_back(i);
                 res[i]=;
             }
         int szindex=cindex.size();

         int count=;
         for(int j=cindex[]-;j>=;j--)           //write the distance before the first C
             res[j]=count++;

         count=;
         for(int k=cindex[szindex-]+;k<len;k++)  //write the distance after the last C
             res[k]=count++;

         for(int x=;x<szindex;x++)                //write the distance between two C
         {
             count=;
             int left=cindex[x-]+,right=cindex[x]-;
             while(left<=right)
             {
                 res[left++]=count;
                 res[right--]=count++;
             }
         }
         return res;
     }
 };