refer to: https://www.algoexpert.io/questions/Longest%20Substring%20Without%20Duplication

Problem Statement

 

 Analysis

 

 Code

def longestSubstringWithoutDuplication(string):
    # Write your code here.
    lastSeen = {}# hashmap to store the index of the lastSeen character(updated index of unique character)
    longest = [0,1] # initialize to itself (since in python the slice function will exclude the right range)
    startIdx = 0 # startIdx to traverse the whole string, update the start character in substring
    for i, char in enumerate(string):
        if char in lastSeen: # duplicate will occur if do nothing
            startIdx = max(startIdx, lastSeen[char] + 1) # update the startIdx, lastSeen character idx + 1 to exclude the lastSeen character
        if longest[1] - longest[0] < i + 1 - startIdx: #update the longest substring
            longest = [startIdx, i + 1] # the i+1 th character will be excluded
        lastSeen[char] = i # update the index of the lastSeen character
    return string[longest[0] : longest[1]]

Time and space complexity