1358. Number of Substrings Containing All Three Characters

容易超时，需要优化，减少重复处理次数。

class Solution {
public:
    
    int process(string& s, vector<int>& a_indexs, char c1, char c2){
        int res = 0;
        for (int i=0;i<a_indexs.size();i++){
            int a_index = a_indexs[i];
            
            // find all b_index>a_index and all c_index>a_index, gain max num
            int b_index = -1;
            for (int j=a_index+1;j<s.size();j++){
                if (s[j]==c1){
                    b_index = j;
                    break;
                }
            }
            
            int c_index = -1;
            for (int j=a_index+1;j<s.size();j++){
                if (s[j]==c2){
                    c_index = j;
                    break;
                }
            }
            
            if (b_index!=-1 && c_index!=-1){
                int max = b_index>c_index?b_index:c_index;
                res += s.size()-max;
            }
        }
        return res;
    }
    
    int numberOfSubstrings(string s) {
        
        vector<int> a_indexs;
        vector<int> b_indexs;
        vector<int> c_indexs;
        for (int i=0;i<s.size();i++){
            if (s[i]=='a'){a_indexs.push_back(i);}
            if (s[i]=='b'){b_indexs.push_back(i);}
            if (s[i]=='c'){c_indexs.push_back(i);}
        }
        
        //gain res
        int res1 = process(s, a_indexs, 'b', 'c');
        int res2 = process(s, b_indexs, 'a', 'c');
        int res3 = process(s, c_indexs, 'a', 'b');
        return res1+res2+res3;
        
    }
};