leetcode 3. Longest Substring Without Repeating Characters Python

leetcode 3. Longest Substring Without Repeating Characters Python

Description

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

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 be a substring, "pwke" is a subsequence and not a substring.

问题分析

本题是一道中等题，意思是给定一个字符串，返回字符串的最长不重复子串.

明白了题目的意思，就知道如何动手去做了，最直接的方法就是进行暴力搜索，我用暴力搜索实现后，又去参考了下别人的实现，改进了下，只需要一重循环即可。

代码实现

暴力搜索实现

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        length = 0
        res = set()
        for i in range(len(s)):
            for j in range(i, len(s)):
                if s[j] not in res:
                    res.add(s[j])
                else:
                    if len(res) > length:
                        length = len(res)
                    res.clear()
                    break
        if len(res) > length:
            length = len(res)
        return length

改进实现

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        max_length = 0
        current_length = 0
        sub = ""
        for i in range(len(s)):
            if s[i] in sub:
                index = sub.index(s[i])
                sub = sub[index + 1:]
                current_length = len(sub)
            sub += s[i]
            current_length += 1
            if current_length > max_length:
                max_length = current_length
        return max_length
        

运行结果对比

从图中可以看出，二者的运行时间相差还是挺多的，因此要善于借鉴别人的优秀代码，慢慢提高自己写代码的能力。

ok!大功告成了，如果你有其他的方法或者问题，欢迎在评论区交流。