FAANG · LeetCode #125

Valid Palindrome — three-stage drill

1The ProblemEasy

Valid Palindrome

Reads the same forwards and backwards (letters & digits only).

Examples

"racecar"→ true"race a car"→ false

2The PatternTIME O(n) · SPACE O(1)

Two Pointers

Converging from both ends, comparing as they meet.

Problems using this pattern

3The SolutionRESULT → true

Step through it

Initialize: left at 0, right at 6.

Step 1 / 5

Python▎two pointers converge

1def isPalindrome(s):
2    s = [c.lower() for c in s if c.isalnum()]
3    left, right = 0, len(s) - 1
4    while left < right:
5        if s[left] != s[right]:
6            return False
7        left += 1
8        right -= 1
9    return True

Arrow keys to navigate · escape to reset

All problems by pattern

Two Pointers

Valid Palindrome
Two Sum II — Sorted Array

Sliding Window

Longest Substring Without Repeating Characters
Minimum Size Subarray Sum

Prefix Sum

Monotonic Deque

Shortest Subarray with Sum at Least K

Binary Search

Arrays & Hashing

Monotonic Stack

Daily Temperatures
Next Greater Element I

Intervals

Valid Palindrome — three-stage drill

Valid Palindrome

Two Pointers

Step through it

All problems by pattern

Two Pointers

Sliding Window

Prefix Sum

Monotonic Deque

Binary Search

Arrays & Hashing

Monotonic Stack

Intervals

Heap / Top-K

Backtracking

Recursive Descent