Leetcode 3. Longest Substring Without Repeating Characters

[medium]

Longest Substring Without Repeating Characters - LeetCode

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

Example 1:

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

Example 2:

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

Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Example 4:

Input: s = ""
Output: 0

Constraints:

• 0 <= s.length <= 5 * 104
• s consists of English letters, digits, symbols and spaces.

[Java]

1. create a hashmap to note the character previous appear
2. if the map already contains the key, we update the begin pointer; if it’s not, add it into the map, and use it index to be the value.
3. scan through the String and record the max substring