C Super-Simple Clean Solution 0ms
\nint lengthOfLongestSubstring(char * s){\n    /*letter_map is to keep track if we saw this character in this substring*/\n    int letter_map[128] = {0}, res = 
```\nint lengthOfLongestSubstring(char * s){\n    /*letter_map is to keep track if we saw this character in this substring*/\n    int letter_map[128] = {0}, res = 0;\n    char* start = s, *end = s;\n    \n    while (*end) {\n        /* If we reached a letter we saw already - check max length and start a new substring*/\n        if (letter_map[*end]) {\n            res = (end - start > res) ? end - start : res;\n            while (*start != *end) {\n                letter_map[*start] = 0;\n                start++;\n            }\n            start++;\n            end++;\n        }\n        else {\n            letter_map[*end] = 1;\n            end++;\n        }  \n    }\n    return end-start > res ? end-start : res;\n}\n```\n**Like it? please upvote...**
['C']