The longest substring without repeating characters.

题目描述

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

Examples

Example 1:

Input: "abcabcbb" 
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3 Explanation: 
The answer is "wke", with the length of 3. Note that the answer must

Solution

首先自己意识到了用HashSet进行添加非重复元素，但出现元素重复时应该删除哪一个却不确定。当出现重复元素时画图分析可知，当前记录String的leftIndex至rightIndex区间内子序列可能并非最长，这时应删除l当前leftIndex所指向元素。让leftIndex++,重新开始计算。

Code

public int lengthOfLongestSubstring(String s) {
      int lIndex = 0, rIndex = 0;
      int n = s.length();
      Set<Character> characterSet = new HashSet<>();
      int maxSubStringLength = 0;
      while (rIndex < n && lIndex < n) {
          char c = s.charAt(rIndex);
          if (!characterSet.contains(c)) {
              characterSet.add(c);
              rIndex++;
              maxSubStringLength = Math.max(maxSubStringLength, rIndex - lIndex);
          } else {
              characterSet.remove(s.charAt(lIndex++));
          }
      }
      return maxSubStringLength;
  }