Question

How to find the longest substring without repeating characters in Python

Answer 1

def findLongestSubstringWithoutRepeatingCharacters(str) :
    str_size = len(str)
    start = 0
    end = 0
    start_sub = 0
    end_sub = 0
    ASCII = [0] * (256)
    
    while (end < str_size) :
        if (ASCII[ord(str[end])] > 0) :
            while (str[start] != str[end]) :
                ASCII[ord(str[start])] = 0
                start += 1
            start += 1
        else :
            ASCII[ord(str[end])] = end + 1
            if (end - start > end_sub - start_sub) :
                start_sub = start
                end_sub = end
        end += 1
        
    i = start_sub
        
    while (i <= end_sub) :
        print(str[i], end ="")
        i += 1
        
str = "xwwwqfwwxqwyq"

findLongestSubstringWithoutRepeatingCharacters(str)

 
 

'''
run:

xqwy

'''

 

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Answer 2

def longest_substring(s: str) -> str:
    start = 0
    max_length = 0
    char_index_map = {}
    longest_substr = ""

    # Iterate through the string
    for end in range(len(s)):
        if s[end] in char_index_map and char_index_map[s[end]] >= start:
            # Move the start pointer to avoid duplicates
            start = char_index_map[s[end]] + 1
        
        # Update the character's latest index
        char_index_map[s[end]] = end
        
        # Check if the current substring is the longest
        current_length = end - start + 1
        if current_length > max_length:
            max_length = current_length
            longest_substr = s[start:end + 1]
    
    return longest_substr


print(longest_substring("abcabcbb"))  # Output: "abc"
print(longest_substring("bbbbb"))    # Output: "b"
print(longest_substring("xwwwqfwwxqwyq"))   # Output: "xqwy"



'''
run:

abc
b
xqwy

'''

 

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