Leetcode 3. Longest Substring Without Repeating Characters思路解析

題目

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.

思路

先以下面這case舉例：
Given “wobgrovw” the answer is “bgrovw”，with the length of 6

令sub_str爲當前迭代的最大連續子字符串， sub_set是歷史的最大連續子字符串
sub_str         sub_set
“w”            []
“wo”          []
“wob”        []
“wobg”       []
“wobgr”      []
“bgro”       [“wobgr”]
“bgrov”      [“wobgr”]
“bgrovw”     [“wobgr”]
“”              [“wobgr”, “bgrovw”]

然後遍歷sub_set 中最長的sub_str，即得到答案

Python實現

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        sub_set = []
        sub_str = ''
        for i in s:
            if i not in sub_str:
                sub_str += i
            elif i == sub_str[0]:
                sub_str = sub_str[1:] + i
            elif i == sub_str[-1]:
                sub_set.append(sub_str)
                sub_str = i
            else:
                sub_set.append(sub_str)
                idx = sub_str.index(i)
                sub_str = sub_str[idx+1:] + i
        if sub_str:
            sub_set.append(sub_str)
        max_sub_len = 0
        for sub_str in sub_set:
            if len(sub_str) > max_sub_len:
                max_sub_len = len(sub_str)
        return max_sub_len

耗時