String Manipulation String Hash Map Counting Character Pattern Matching
Intermediate Level

Implement the longestSubstringNoRepeat method that returns the length of the longest substring without repeated characters.

The input contains a string text. Your task is to return the length of the longest substring that does not contain any repeated character.

A substring must be continuous. For example, in abcabcbb, the longest substring without repeating characters is abc, so the answer is 3.

Example 1
Input:
text (string) = abcabcbb
Return:
(int) 3
Example 2
Input:
text (string) = bbbbb
Return:
(int) 1
Example 3
Input:
text (string) = pwwkew
Return:
(int) 3

Use a sliding window to keep a substring with unique characters.

Move the right side of the window one character at a time. If the current character was already seen inside the current window, move the left side just after the previous occurrence of that character.

After each step, update the maximum window length.

Pseudocode:

function longestSubstringNoRepeat(text):
    lastSeen = empty map
    left = 0
    best = 0
    for right from 0 to length(text) - 1:
        ch = text[right]
        if ch exists in lastSeen and lastSeen[ch] >= left:
            left = lastSeen[ch] + 1
        lastSeen[ch] = right
        best = max(best, right - left + 1)
    return best
Run your code to see the result.