C++|clean and simple with important comments
we just need to find the longest substring wth atmax 1 character occuring odd number of times\n\nclass Solution {\npublic:\n    int longestAwesome(string s) {\n
we just need to find the longest substring wth atmax 1 character occuring odd number of times\n```\nclass Solution {\npublic:\n    int longestAwesome(string s) {\n        int n = s.length();\n        unordered_map<int,int>M;\n        M[0] = -1;\n        int mask = 0;\n        int max_len = 0;\n        for(int i = 0;i < n; i++)\n        {\n            mask ^= (1 << (s[i] - \'0\'));\n            if(M.find(mask) == M.end())\n                M[mask] = i;\n            else//all the character are of even occurances\n            {\n                max_len = max(max_len, i - M[mask]);\n                \n            }\n\t\t\t//at max 1 occurance of a character is fine \n            for(int j = 0; j <= 9; j++)\n            {\n                if(M.find(mask ^ (1 << j)) != M.end())\n                    max_len = max(max_len, i - M[mask ^ (1 << j)]);\n            }\n        }\n        return max_len;\n        \n    }\n};\n```
['Bit Manipulation']