[LeetCode] Longest Substring Without Repeating Characters

[题目]

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.

 

 

 

[解题思路0]

 

 

 

扫描遇到重复字母时，以上一个重复字母的index + 1，作为新的搜索起始位置。

 

[解题思路1]

 使用LinkedHashSet作为移动窗口，这样可以节省空间

 代码如下：

 

public int lengthOfLongestSubstring(String s) {
  if (s.length() == 0) return 0;
  int ret = 1;
  Set<Character> set = new LinkedHashSet<Character>();
  int[] maxEndsWith = new int[s.length()];
  maxEndsWith[0] = 1;
  set.add(s.charAt(0));
  for (int i = 1; i < s.length(); ++i) {
    char c = s.charAt(i);
    if (!set.contains(c)) {
      set.add(c);
      maxEndsWith[i] = maxEndsWith[i - 1] + 1;
    } else {
      Iterator<Character> it = set.iterator();
      while (it.hasNext()) {
        char front = it.next();
        it.remove();
       if (front == c) break;
      }
      set.add(c);
      maxEndsWith[i] = set.size();
      }
     ret = Math.max(maxEndsWith[i], ret);
   }
   return ret;
}