1371. Find the Longest Substring Containing Vowels in Even Counts

class Solution {
public:
    map<char,int> s = {{'a',0},{'e',1},{'i',2},{'o',3},{'u',4}};

    int findTheLongestSubstring(string str) {
        int mask=0;
        vector<int> pre;
        for(auto e : str){
            if(s.find(e) != s.end()){
                mask = mask ^ (1<<(e-'a'));
            }
            pre.push_back(mask);
        }

        // for(auto e : pre) cout << e << " ";

        map<int,int> m; m[0] = -1;
        int ans=0;
        for(int i=0; i<pre.size(); i++){
            auto e = pre[i];
            if(m.find(e) == m.end()){
                m[e] = i;
            }

            ans = max(ans, i-m[e]);
        }

        return ans;
    }
};


// xor
// bit unchagned
// 0 0 0
// 1 0 1
// bit flip 
// 0 1 1
// 1 1 0