3. Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

Examples:

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

本题是典型的动态规划问题。

主干思想：以abcabcbb为例，这个字符串的最大字串是 （不包含最后一个b的剩余字符串的abcabcb的最大字串） 和 （包含最后一个b的最大不重复字串）中较大值。

编写程序实现。

 dynamic函数中的形参last表示字符串s的最大下标，及长度减去1的值。因为在c语言中仅仅通过s无法知道它的大小。

calcul_include_last函数用于计算包含最后一个字符的最长不重复子串。formor表示包含最后一个字符的最长不重复子串的左下标。

int calcul_include_last(char *s, int last) {
    int formor = 0;
    for(int i=last; i>formor; i--) {
        for(int j=i-1; j>=formor; j--)
        if(s[i]==s[j]) {formor = j+1; break;}
    }
    return last-formor+1;
}

int dynamic(char *s, int last) {
    if (last==0) return 1;
    
    int compare1 = dynamic(s, last-1);
    int compare2 = calcul_include_last(s, last);
    if(compare1 > compare2) 
        return compare1;
    else 
        return compare2;
}

int lengthOfLongestSubstring(char* s) {
    if(!strlen(s)) return 0;
    
    return dynamic(s, strlen(s)-1);
}