TheAlgorithms-C/leetcode/src/3.c

int lengthOfLongestSubstring(char* str) {

    int n = strlen(str);

    if(!n) return 0;

    int L_len = 1;          // lenght of longest substring
    int C_len = 1;          // lenght of current substring

    int P_ind, i;           //  P_ind for previous index
    int visited[256];       //  visited will keep track of visiting char for the last instance.
                            //  since there are 256 ASCII char, its size is limited to that value.
    memset(visited, -1, sizeof(int) * 256);
    visited[str[0]] = 0;        //  the index of that char will tell us that when it was visited.
    for (i = 1; i < n; i++)
    {
        P_ind =  visited[str[i]];
        if (P_ind == -1 || i - C_len > P_ind)
            C_len++;        //  if the current char was not visited earlier, or it is not the part of current substring
        else
        {                           //  otherwise, we need to change the current/longest substring length
            if (C_len > L_len) L_len = C_len;
            C_len = i - P_ind;
        }
        visited[str[i]] = i;
    }
    if (C_len > L_len) L_len = C_len;
    return L_len;
}
/* Brute force */
int lengthOfLongestSubstring(char * s){
    int cur_max = 0, max = 0;
    int counter[255];
    int end = 0;

    memset(counter, 0, sizeof(int) *255);
    while (end < strlen(s)) {
        if (counter[s[end]] == 0) {
            counter[s[end]]++;
            end++;
            cur_max++;
        } else {
            char c = s[end];
            memset(counter, 0, 255 * sizeof(int));
            if (cur_max >= max)
                max = cur_max;
            cur_max = 0;
            while(s[end - 1] != c)
                end--;
        }
    }
    if (cur_max >= max)
        max = cur_max;
    return max;
}