[leetcode] 3. Longest Substring Without Repeating Characters

题目

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.

Constraints:

• 0 <= s.length <= 5 * 10^4
• s consists of English letters, digits, symbols and spaces.

思路

双指针，遍历字符串，用一个字典存储每个字符的最新位置，且每次遍历时保存最长长度。当当前字符在字典中且位置小于等于左指针所在的位置时，左指针跳至字典位置进一的位置，表示新的不重复字符串，直至遍历结束。

代码

python版本：

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        used_chars={}
        max_count=0
        l=0
        for i,char in enumerate(s):
            if char in used_chars and used_chars[char]>=l:
                l=used_chars[char]+1
            else:
                max_count=max(max_count,i-l+1)
            used_chars[char]=i
        return max_count