3. Longest Substring Without Repeating Characters

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.

解题要点：

用一个dictionary来记录每个字符的index，然后有左右两个指针指向最大长度的字符串。在遍历字符时，如有重复的，把左指针更新为之前dict里字符index的后一位，最后计算长度，记录最长。

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        mydict = {}
        j = 0
        maxNum = 0
        for i in range(len(s)):
            if s[i] in mydict:
                j = max(j, mydict[s[i]] + 1)
            mydict[s[i]] = i
            maxNum = max(maxNum, i-j+1)
        return maxNum