C++ Easy to understand solution (72ms) O(n)

  • 0
        unordered_map<char,int> map; //Create a hash table with stl map.
        int result;
        for(int i = 0; i < input.length(); i++) //Insert in the map all characters of the string.
        for(int j = 0; j < input.length(); j++) //Loop through again to check.
            if(map[input[j]] == 1) //If character is already in the map, then it is the unique one.
            result = j;
            return result;
    return -1;

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