[Leetcode]question 3: Longest Substring without Repeating Characters

Title: Longest Substring without Repeating Characters

Description:

Given a string, find the length of the longest substring without repeating characters.

 

Analysis:

1. list all the substrings exhaustily.

2. insert i, j as start and end poster.then justify if the substring has no repeating characters.

time spends: o(n^2). space spend:o(n)

3. improved from (2), if the j th has been appeared in the i-j substring, j will be added in and i should auto-increased to  non-repeating.

that is to say: in given input = "abcb", when i =0, j =3, abcb has repeating'b', we will set i++ until to 2, at this time, i = 2, j =3."cb"

4. improved from (3). we can use hashmap to store the index of the redundancy character rather than auto-increase.

 

for 3).

answer will be:

package com.connie;

import java.util.HashSet;
import java.util.Set;

public class Leetcode3 {

    public static void main(String[] args) {
 // write your code here
      System.out.print(longSubString("pwwkew")+","+longSubString("abcabcbb"));
    }
    private static int longSubString(String str) {
      int longest = 1, i = 0, j = 1;
      Set subStr = new HashSet();
      subStr.add(str.charAt(i));
      while(i<str.length() && j<str.length()){

        if(!subStr.contains(str.charAt(j))){
          subStr.add(str.charAt(j++));
          longest = Math.max(longest, j-i);

        } else {
//          if(i+1 == j) {
//            j++;
//            i++;
//          } else {
            subStr.remove(str.charAt(i++));
//          }
        }
      }
      return longest;
    }
}

for 4)..

package com.connie;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class Leetcode3 {

    public static void main(String[] args) {
 // write your code here
      System.out.print(longSubString("pwwkew")+","+longSubString("abcabcbb"));
    }
    private static int longSubString(String str) {
      int longest = 1, i = 0, j = 1;
      Map subStr = new HashMap();
      subStr.put(str.charAt(i), i);
      while(i<str.length() && j<str.length()) {
        if(subStr.containsKey(str.charAt(j))) {
          i = (Integer) subStr.get(str.charAt(j))+1;
        }
        subStr.put(str.charAt(j), j);
        j++;
        longest = Math.max(longest, j-i);
      }
      return longest;
    }
}