[LeetCode] Longest Substring without repeat characters

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.

Java Code

public int lengthOfLongestSubstring(String s) {
         int startIndex = 0;
           boolean[] visited = new boolean[256];
           int maxLen = 0;
           
           for(int i = 0; startIndex <= i && i < s.length(); i++){
               char a = s.charAt(i);
               if(!visited[a]) {
                   visited[a] = true;
               }else{
                   maxLen = maxLen > (i+1-startIndex)? maxLen : i + 1 - startIndex;
                   while(s.charAt(startIndex) != a ) {
                        visited[s.charAt(startIndex)] = false;
                       startIndex++;
                   }
                   
                   startIndex++;
               }
                   
           }
           
           maxLen = maxLen > s.length() - startIndex? maxLen : s.length() - startIndex;
           
           return maxLen;
    }

［Leetcode］ Implement strStr

Implement strStr().
Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

Thoughts:
1. The most straight thought is to iterate through the haystack.
2. 另外一个为kmp算法，讲解可以参考 topcoder

Java Code:

public String strStr(String haystack, String needle) {
         if(needle.length() == 0) return haystack;
         
         int n = 0;
         
         for(int i = 0; i <= haystack.length() - needle.length(); i++){
             n = 0;
             
             while(n < needle.length() && haystack.charAt(i+n) == needle.charAt(n))
                  n++;
                  
             if(n == needle.length()) return haystack.substring(i);
         }
         
         return null;
    }