Most frequently asked interview question #1 with solution

Given a string, find the length of the longest substring without repeating characters.

Solution in C++:

    int lengthOfLongestSubstring(string s) {
       
            int *char_index = (int*)malloc(sizeof(int) * 256);
            int  max_len    = 1;
            int  cur_len    = 1;
       
        if(s.length() == 0){
            return 0;
        }
        //Initializing all the index values with -1 which means the character never appaered before
        for(int iter = 0; iter < 256; ++iter){
           
            char_index[iter] = -1;
        }
       
        //Assigning first character index as 0
        char_index[s[0]] = 0;
       
        //Iterating over each character and keeping track of max lenght
        for(int iter = 1; iter < s.length(); ++iter){
               
                int prev_index = char_index[s[iter]];
           
            //Either the character is encountered for the first time or the character was part of       previous sub string
            if((prev_index == -1) || (iter - cur_len > prev_index)){
               
                ++cur_len;
                cout<<"current lenght is: "<<cur_len<<endl;
            } else {
               
                if(cur_len > max_len){
                    max_len = cur_len;
                }
                cur_len = iter - prev_index;
            }
           
            char_index[s[iter]] = iter;
           
        }
        if(cur_len > max_len){
            max_len = cur_len;
        }
       
        free(char_index);
        return max_len;
    }