输入: S = "loveleetcode", C = 'e'
输出: [3, 2, 1, 0, 1, 0, 0, 1, 2, 2, 1, 0]
说明:

class Solution {
public:
    vector<int> shortestToChar(string S, char C) {
        vector<int> cc;
        int len=S.size();
        vector<int> index;
        for(auto i:S)
            if(i==C) {cc.push_back(0);
                      index.push_back(cc.size()-1);}
            else cc.push_back(len);
        int start=1;
        for(int i=index[0]+1;i<len;i++)
            if(cc[i]) cc[i]=start++;
            else start=1;
        start=1;
        for(int i=index[index.size()-1]-1;i>=0;i--)
            if(cc[i]) cc[i]=min(cc[i],start++);
            else start=1;
        return cc;
    }
};