Description
Total Accepted: 283937
Total Submissions: 1178327
Difficulty: Medium
Contributor: LeetCode
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.

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package string;

public class LengthOfLongestSubstring {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
      String[] tests = {"ctnlk", "z", "aaaa", "aab", "", "an++--viaj"};
      int[] res = {5, 1, 1, 2, 0, 5};
      for (int i = 0; i < tests.length; i++) {
          int ans = lengthOfLongestSubstring(tests[i]); 
          System.out.println(ans == res[i]);
      }
    }
    
    public static int lengthOfLongestSubstring(String s) {
      int[] map = new int[256]; // map from character's ASCII to its last occured index
      int j = 0;
      int len = 0;
      for (int i = 0; i < s.length(); i++) {
          while (j < s.length() && map[s.charAt(j)] == 0) {
              map[s.charAt(j)] = 1;                   
              len = Math.max(len,  j - i + 1);
              j++;
          }
          map[s.charAt(i)] = 0;
      }
      return len;
    }
    
    
    public static int lengthOfLongestSubstring_failed(String s) {
        if (s == null || s.length() == 0 || s.length() == 1) return s.length();
        int len = 0;
        char[] arr = s.toCharArray();
        
        int j = 0;
        for (int i = 0; i < s.length(); i++) {
                while (j < s.length()) {
                  if(j < s.length() && arr[i] != arr[j]) {
                    // System.out.printf("arr[%d] = %c \t", j, arr[j]);
                    len = Math.max(len, j - i + 1);
                    j++;
                  } 
                  if (j < s.length() && arr[i] == arr[j]) {
                    len = Math.max(len, j - i );
                    i = j;
                    j++;
                  }              
                }
            }
        
        return len;
    }
}