[leetcode: Python]3. Longest Substring Without Repeating Characters

Title:
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.
题目大意：
给定一个字符串，从中找出不含重复字符的最长子串的长度。例如，”abcabcbb”的不含重复字母的最长子串为”abc”，其长度是3。”bbbbb”的最长子串是”b”，长度为1。

解题思路：
“滑动窗口法”

变量start和end分别记录子串的起点和终点

从左向右逐字符遍历原始字符串，每次将end + 1

字典countDict存储当前子串中各字符的个数

当新增字符c的计数 > 1时，向右移动起点start，并将s[start]在字典中的计数 - 1，直到countDict[c]不大于1为止

更新最大长度

(怎么LeetCode上居然没有其他使用python的答案吗。。还是我电脑的问题？)
方法一：98ms

class Solution:
    # @return an integer
    def lengthOfLongestSubstring(self, s):
        ans, start, end = 0, 0, 0
        countDict = {}
        for i in s:
            end += 1
            countDict[i] = countDict.get(i, 0) + 1
            while countDict[i] > 1:
                countDict[s[start]] -= 1
                start += 1
            ans = max(ans, end - start)
        return ans