DSAverse

Two Pointers & Sliding Window

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Two Sum Pattern

2 + 6 = 8

L=0target: 10R=9

3Sum

Sort the array, fix a pivot (yellow), then sweep two pointers from both ends of the remaining subarray. Duplicates are skipped automatically to keep triplets unique.

Visualization

Speed

—

Pivot

—

Current sum

Triplets found

-4

–

-1

–

-1

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Pivot (P)Left pointer (L)Right pointer (R)Triplet foundAlready processed

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Complexity

O(n²)

Best Case

O(n²)

Worst Case

O(n log n)

Sorting

O(1)

Space

How It Works

1Sort the array so duplicates are adjacent and two-pointer decisions are valid
2Fix pivot i from 0 to n−3; skip if nums[i] == nums[i−1]
3Set left = i+1, right = n−1. Compute sum = nums[i]+nums[left]+nums[right]
4If sum == 0: record triplet, skip duplicate left/right values, move both inward
5If sum < 0: left++ (need larger). If sum > 0: right-- (need smaller)

Active Recall Quiz

Question 1 of 3