LeetCode : Longest Substring Without Repeating Characters [java]

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.

思路：目标是找到一个最长的不包含重复字母的子串，使用Hashtable保存已经出现但未重复的字符，start记录当前子串起始位置，end记录结束位置。

遍历字符串：

1. 如果当前字符未出现，则加入Hashtable（键为字符，值为下标），同时更新已找到最长字符串的长度max；

2. 如果当前字符已经出现了，则子串起点位置start移到该字符首次出现位置的下一个位置，同时从Hashtable中移除当前start位置之前存放的字符记录，将该字符新位置加入Hashtable，更新max；

import java.util.Hashtable;

public class Solution {
public int lengthOfLongestSubstring(String s) {
Hashtable<String, Integer> existTable = new Hashtable<>();
int start = 0;
int end = 0;
int max = 0;
for (int i = 0; i < s.length(); i++) {
end++;
String str = s.substring(i, i + 1);
if (existTable.containsKey(str)) {
int startOld = start;
start = existTable.get(str) + 1;
for (int j = startOld; j < start; j++) {
String toRemove = s.substring(j, j + 1);
existTable.remove(toRemove);
}
}
existTable.put(str, i);
max = end - start > max ? end - start : max;
}
return max;
}
}