3Sum Closest — LeetCode #16 | Python Algorithm Visualization

Published: 05 July 2026
on channel: Benabub

Step-by-step algorithm visualization for LeetCode #16 (3Sum Closest). The solution first sorts the input array to enable a two-pointer search pattern. For each element, we fix it as a base and use two pointers to scan the remaining array, dynamically tracking the sum with the smallest absolute difference to the target.

Complexity Analysis:
Time Complexity: O(n^2) — sorting takes O(n log n), and the nested two-pointer traversal takes O(n^2) in the worst case.
Space Complexity: O(1) — excluding the input sorting overhead, we use only constant extra memory for pointers and tracking variables.

Timestamps:
0:00 — Array Sorting & Initial Setup
0:14 — `i==0`: Outer Loop & Duplicate Skip Logic
0:19 — `i==0`: Two-Pointer Scan & Closest Sum Update
0:53 — `i==1`
2:25 — `i==2`
2:36 — `i==3`
3:42 — `i==4`
4:15 — Return Result

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