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Monday, December 24, 2012

[LeetCode] Longest Substring Without Repeating Characters 解题报告


Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest substring is "b", with the length of 1.
» Solve this problem

[解题思路]
从左往右扫描,当遇到重复字母时,以上一个重复字母的index +1,作为新的搜索起始位置。比如

直到扫描到最后一个字母。


[Code]
Version 1
1:    int lengthOfLongestSubstring(string s) {  
2:      // Start typing your C/C++ solution below  
3:      // DO NOT write int main() function  
4:      int count[26];  
5:      if(s.size() ==0) return 0;  
6:      memset(count,-1, sizeof(count));  
7:      int start = 0;  
8:      int maxV = 0;  
9:      for(int i=0; i< s.size(); i++)  
10:      {  
11:        int index = s[i] - 97;  
12:        if(count[index] >= 0)  
13:        {            
14:          if(maxV < (i -start))  
15:          {  
16:            maxV = i-start;  
17:          }  
18:          i = count[index];  
19:          start = i+1;  
20:          memset(count,-1, sizeof(count));  
21:          continue;  
22:        }  
23:        count[index] = i;  
24:      }  
25:      if(maxV < (s.size() -start))  
26:      {  
27:        maxV = s.size()-start;  
28:      }  
29:      return maxV;  
30:    }  


Version 2, refactor the code at 3/4/2013
1:       int lengthOfLongestSubstring(string s) {  
2:            int count[26];  
3:            memset(count, -1, 26*sizeof(int));  
4:            int len=0, maxL = 0;  
5:            for(int i =0; i< s.size(); i++,len++)  
6:            {  
7:                 if(count[s[i]-'a']>=0)  
8:                 {  
9:                      maxL = max(len, maxL);  
10:                      len =0;          
11:                      i = count[s[i]-'a']+1;  
12:                      memset(count, -1, 26*sizeof(int));   
13:                 }  
14:                 count[s[i]-'a']=i;  
15:            }      
16:            return max(len, maxL);  
17:       }  

Note:
1. Line 3, since we store the index in array, so initializing the array as 0 will mistake the logic.
2. Line 16, catch the last string. for example, "abcd", if no Line 16, it will just return 0 since the Line 9 won't be triggered.

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