leetcode-#3 Longest Substring Without Repeating Characters_main() { char s[]={"abcdefghijklmn!"},*sp=s; in

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

Example 1:

Input: “abcabcbb”
Output: 3
Explanation: The answer is “abc”, with the length of 3.

Example 2:

Input: “bbbbb”
Output: 1
Explanation: The answer is “b”, with the length of 1.

Example 3:

Input: “pwwkew”
Output: 3
Explanation: 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.

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/longest-substring-without-repeating-characters
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
The code writen in leetcode, this snapshot code could pass the examination.

int lengthOfLongestSubstring(char * s){
    int maxlen = 0, currlen = 0;
    int table[256] = {0}, i = 0, j = 0, start = 0;
    int num = 0;
    
    for (i=0; s[i] != '\0'; i++)
    {
        num = ++table[s[i]];
        if (num == 2)
        {
            if (currlen > maxlen)
            {
                maxlen = currlen;
            }
            
            for (j = start; j < i; j++)
            {
                if (s[j] == s[i])
                {
                    table[s[j]] = 1;
                    start = j + 1;
                    break;
                }
                else
                {
                    --currlen;
                    table[s[j]] = 0;
                }
            }
        }
        else
        {
            ++currlen;
        }
    }
    
    if (currlen > maxlen)
    {
        maxlen = currlen;
    }
    
    return maxlen;
}
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The testing code as follow:

#include <stdio.h>
#include <string.h>

int lengthOfLongestSubstring(char * s){
    int maxlen = 0, currlen = 0;
    int table[256] = {0}, i = 0, j = 0, start = 0;
    int num = 0;
    
    for (i=0; s[i] != '\0'; i++)
    {
        num = ++table[s[i]];
        if (num == 2)
        {
            if (currlen > maxlen)
            {
                maxlen = currlen;
            }
            
            for (j = start; j < i; j++)
            {
                if (s[j] == s[i])
                {
                    table[s[j]] = 1;
                    start = j + 1;
                    break;
                }
                else
                {
                    --currlen;
                    table[s[j]] = 0;
                }
            }
        }
        else
        {
            ++currlen;
        }
    }
    
    if (currlen > maxlen)
    {
        maxlen = currlen;
    }
    
    return maxlen;
}

int main()
{
	char *s1 = "abcdefghijklmnabcdefgha";
	char *s2 = "abcdefghijklmnopqrstuvwxyz";
	int result = 0;

	result = lengthOfLongestSubstring(s1);
	printf("The string s1 is %s \n and the lengthOfLongestSubstring is %d\n", s1, result);
	
	result = lengthOfLongestSubstring(s2);
	printf("The string s2 is %s \n and the lengthOfLongestSubstring is %d\n", s2, result);

	return 0;
}
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The executing result is :

hanwu@hanwu:/media/hanwu/Software/work/leetcode/lengthOfLongestSubstring$ gcc lengthOfLongestSubstring.c 
hanwu@hanwu:/media/hanwu/Software/work/leetcode/lengthOfLongestSubstring$ ./a.out 
The string s1 is abcdefghijklmnabcdefgha 
 and the lengthOfLongestSubstring is 14
The string s2 is abcdefghijklmnopqrstuvwxyz 
 and the lengthOfLongestSubstring is 26
hanwu@hanwu:/media/hanwu/Software/work/leetcode/lengthOfLongestSubstring$
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方法二：

int lengthOfLongestSubstring(char * s){ 
    int accept = 0, maxlen = 1, unrepeatnum = 1;
    int start = 0;
    char *arr = s;
    int i, j;

    if (arr[0] == '\0')
        return 0;

    for(i = 1; s[i] != '\0'; i++)
    {
       accept = 1;

       for(j = start; j < i; j++)
       {
            if (arr[j] == arr[i])
            {
                accept = 0;
                break;
            }
        }

        if(accept)
        {
            unrepeatnum++; 
        }   
        else
        {
            start = ++j;
            unrepeatnum = i - start + 1;
        }

        if(unrepeatnum > maxlen)
        {   
            maxlen = unrepeatnum;
        }   
    }   

    return maxlen;
}
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方案三：

int lengthOfLongestSubstring(char * s){ 
    int accept = 0, maxlen = 1, unrepeatnum = 1;
    char *start, *ptr;
    char *arr = s;

    if (arr[0] == '\0')
        return 0;

    arr++;
    for (start = s; *arr != '\0'; arr++)
    {   
        accept = 1;
        for (ptr = start; ptr < (start + unrepeatnum); ptr++)
        {   
            if (*ptr == *arr)
            {   
                accept = 0;
                break;
            }   
        }   

        if (accept)
        {   
            unrepeatnum ++; 
        }   
        else
        {   
            start = ++ptr;
            unrepeatnum = arr - start + 1;
        }   

        if (unrepeatnum > maxlen)
        {   
            maxlen = unrepeatnum;
        }   
    }   

    return maxlen;                                                                                                                                                                                          
}
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