Today, let's break down another LeetCode challenge that uses terms that might be unfamiliar or confusing. As always, understanding the problem is half the battle!
The Original Challenge
Here's how LeetCode presents the problem:
Given a string
s, find the length of the longest substring without repeating characters.
Example:
Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.
Let's break down why this language might be confusing:
"substring" vs "subsequence" - What's the difference?
"without repeating characters" - Does order matter?
"longest" - Do we need to find the actual substring or just its length?
The Challenge in Plain English
Think of it like finding the longest stretch of unique letters in a word. For example:
Take the word "strawberry":
s t r a w b e r r y
We need to:
Find sections where no letter repeats
These sections must be continuous (no skipping letters)
Find the longest such section
Connecting the Technical to the Simple
Let's match the formal language to our simple explanation:
| LeetCode Says | In Plain English |
| "substring" | A continuous section of the string, like taking a bite out of it |
| "without repeating characters" | Every character in our section must be unique |
| "longest" | We want the biggest such section we can find |
| "subsequence" | A series of characters that can skip letters (which is NOT what we want) |
Key Points to Understand
"Substring" means:
Characters must be consecutive
Can't skip characters
Like highlighting a section of text
"Without repeating" means:
Each character can only appear once
'aab' is not valid because 'a' repeats
'abc' is valid because all characters are unique
"Longest" means:
We want the maximum length
Multiple valid answers? Pick the longest
Only need to return the length, not the substring itself
Common Misunderstandings
"I need to find all possible substrings"
No! We only need the length of the longest one
Don't need to store all possibilities
"It's asking for a subsequence"
No! 'pwke' in "pwwkew" is not valid
Must be consecutive characters
"I need to return the substring"
No! Just return the length
The actual substring isn't required
Practical Example
Let's examine "pwwkew":
p w w k e w
Let's find all valid substrings:
"p" (length 1)
"pw" (length 2)
"w" (length 1)
"wk" (length 2)
"wke" (length 3)
"kew" (length 3)
Answer is 3, because "wke" and "kew" are the longest valid substrings.
Questions to Ask Yourself
"For any position in the string..."
How do I know if I've seen a character before?
How far can I go before seeing a repeat?
"When I find a repeat..."
What length should I record?
Where should I start looking next?
"About the current substring..."
Is it continuous?
Are all characters unique?
Is it longer than what I've found before?
Why the Language Matters
LeetCode's use of technical terms like "substring" vs "subsequence" is intentional:
"Substring" means consecutive characters
"Subsequence" allows skipping characters
This distinction completely changes how we approach the problem
Conclusion
Before coding, make sure you understand:
We need consecutive characters (substring)
Each character can appear only once
We only need the length, not the actual substring
Multiple answers? Length of longest wins
Remember: Taking time to understand these distinctions saves debugging time later! And, will allow for finding a simple solution to the problem.