Longest Substring Without Repeating Characters

Longest Substring Without Repeating Characters leetcode

Medium

Given a string, find the length of the longest substringwithout 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.

Code

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        start = -1
        max = 0
        # dictionary d
        d = {} 
        for i in range(len(s)):
            if s[i] in d and d[s[i]] > start:
                start = d[s[i]]
                d[s[i]] = i
            else:
                d[s[i]] = i
                if i - start > max:
                    max = i - start
        return max
        

Sample 3 Explaination

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.

Start state: d = {} start = -1(because if  string s is empty ,return 1,if start = 0,then i - start = 0,so initialize start = -1) ,max = 0(longest substring without repeating characters)

 

i	d	start	max
i = 0	{'p':0}	-1	1
i = 1	{'p':0,'w':1}	-1	2
i = 2	{'p':0,'w':2}	1	2
i = 3	{'p':0,'w':2,'k':3}	1	2
i = 4	{'p':0,'w':2,'k':3,'e':4}	2	1
i = 5	{'p':0,'w':5,'k':3,'e':4}	2	3