Pointer And Sliding Window

5 problems in this category

Two Pointers String Array Greedy Sliding Window Hash Map

Valid Palindrome

Determine if string is a palindrome, ignoring non-alphanumeric characters and case.

Easy LeetCode
Time: O(n)
Space: O(1)
Example: "A man, a plan, a canal: Panama" → true
Two Pointers String
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Two Sum II - Input Array Is Sorted

Find two numbers in sorted array that add up to target. Return 1-indexed positions.

Medium LeetCode
Time: O(n)
Space: O(1)
Example: [2,7,11,15], target=9 → [1,2]
Two Pointers Array
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Best Time to Buy and Sell Stock

Find maximum profit from buying and selling stock once.

Easy LeetCode
Time: O(n)
Space: O(1)
Example: [7,1,5,3,6,4] → 5 (buy at 1, sell at 6)
Two Pointers Greedy
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Longest Substring Without Repeating Characters

Find the length of the longest substring without repeating characters.

Medium LeetCode
Time: O(n)
Space: O(k)
Example: "abcabcbb" → 3 ("abc")
Sliding Window Hash Map
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Trapping Rain Water

Calculate how much water can be trapped after raining given elevation heights.

Hard LeetCode
Time:
O(n)?
Why O(n)?
Single pass with two pointers moving towards center
We visit each element exactly once. Each position is processed when either left or right pointer reaches it.
Example: Array of 12 elements needs exactly 12 operations (6 from each pointer)
Space:
O(1)?
Why O(1)?
Only using a few variables regardless of input size
We only store left_max, right_max, and two pointers - constant space that doesn't grow with input.
Example: Same memory usage for array of 10 or 10,000 elements
Example: [0,1,0,2,1,0,1,3,2,1,2,1] → 6
Two Pointers Array
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