leetcode-【中等题】3. Longest Substring Without Repeating Characters

题目：

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.

链接：https://leetcode.com/problems/longest-substring-without-repeating-characters/

答案：

参考了这个链接后才明白解题思路，然后依据自己的理解写了代码。

大致思路是：从当前字符开始，往前看，没有出现过重复字符的字符串

代码：

#define MAX_LETTER_NUM 255
class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if(s.empty())
        {
            return 0;
        }
        
        bool exist[MAX_LETTER_NUM];
        int position[MAX_LETTER_NUM];
        int index,rangeIndex;
        int maxLen = 0;
        int start = 0;
        
        for(index = 0; index < MAX_LETTER_NUM; ++ index)
        {
            exist[index] = false;
            position[index] = 0;
        }
        
        for(index = 0; index < s.size(); ++ index)
        {
            if(exist[s[index]])
            {
                for(rangeIndex = start; rangeIndex <= position[s[index]]; ++ rangeIndex)
                {
                    exist[s[rangeIndex]] = false;
                }
                start = position[s[index]] + 1;
                exist[s[index]] = true;
            }else
            {
                exist[s[index]] = true;
                maxLen = (maxLen < index - start + 1) ? index - start + 1:maxLen;
            }
            
            position[s[index]] = index;
        }
        
        return maxLen;
    }
};