Find longest sub string without duplicate character.

longest_nodup_substr.cpp

int lengthOfLongestSubstring(string s) {
    if(s.empty()) return 0;
    int len = s.length();
    int arr[256];
    for(int i=0; i<256; ++i)
        arr[i] = -1;
    int curStart = 0, curLen = 1;
    int maxLen = 1;
    for(int i=0; i<len; ++i) {
        if(arr[s.at(i)] < curStart)
        {
            // current char shown before curStart
            // update its index and update the curLen
            arr[s.at(i)] = i;
            curLen = i - curStart +1;
        }
        else {
            // current char shown after the curStart
            // it's a dup in the current string under investigation
            // update the curLen, reset the curStart
            curLen = i - curStart;
            curStart = arr[s.at(i)] + 1;
            arr[s.at(i)] = i;
        }
        if(maxLen < curLen)
            maxLen = curLen;
    }
    return maxLen;
}