[LeetCode][003] Longest Substring Without Repeating Characters

/*
 * 1. within range [0, i], [beg, end] is the longest substring, and
 *    [candidate, i] is the possible longer substring.
 * 2. extend range to [0, i + 1], if s[i + 1] can be combined with
 *    [candidate, i] AND if [candidate, i + 1] is longer than [beg, end],
 *    update [beg, end].
 * 3. extend range until [0, strlen(s) - 1], the final [beg, end] is the
 *    longest substring without repeating characters.
 */
int lengthOfLongestSubstring(char* s)
{
        int N = strlen(s);
        int beg = 0;
        int end = 0;
        int candidate = 0;
        char c;
        int i, j;

        if (N == 0)
                return 0;

        for (i = 1; i < N; i++) {
                c = s[i];
                for (j = candidate; j <= i - 1; j++) {
                        if (s[j] == c) {
                                candidate = j + 1;
                                break;
                        }
                }
                if (i - candidate > end - beg) {
                        beg = candidate;
                        end = i;
                }
        }

        return end - beg + 1;
}