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

題目：

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.

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

答案：

參考了這個連接後才明白解題思路，而後依據本身的理解寫了代碼。

大體思路是：從當前字符開始，往前看，沒有出現太重複字符的字符串

代碼：

 1 #define MAX_LETTER_NUM 255
 2 class Solution {
 3 public:
 4     int lengthOfLongestSubstring(string s) {
 5         if(s.empty())
 6         {
 7             return 0;
 8         }
 9         
10         bool exist[MAX_LETTER_NUM];
11         int position[MAX_LETTER_NUM];
12         int index,rangeIndex;
13         int maxLen = 0;
14         int start = 0;
15         
16         for(index = 0; index < MAX_LETTER_NUM; ++ index)
17         {
18             exist[index] = false;
19             position[index] = 0;
20         }
21         
22         for(index = 0; index < s.size(); ++ index)
23         {
24             if(exist[s[index]])
25             {
26                 for(rangeIndex = start; rangeIndex <= position[s[index]]; ++ rangeIndex)
27                 {
28                     exist[s[rangeIndex]] = false;
29                 }
30                 start = position[s[index]] + 1;
31                 exist[s[index]] = true;
32             }else
33             {
34                 exist[s[index]] = true;
35                 maxLen = (maxLen < index - start + 1) ? index - start + 1:maxLen;
36             }
37             
38             position[s[index]] = index;
39         }
40         
41         return maxLen;
42     }
43 };

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