代码实现：

解法一：暴力法

int lengthOfLongestSubstring(char *s) {
    int hash[256] = {0};
    int num = 0;
    for (int i = 0; i < strlen(s); i++) {
        int count = 0;
        for (int j = i; j < strlen(s); j++) {
            if (hash[s[j]] == 0) {
                hash[s[j]]++;
                count++;
                num = num > count ? num : count;
            } else {
                memset(hash, 0, sizeof(hash));
                break;
            }
        }
    }
    return num;
}