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3Sum
Learn how to solve the '3Sum' problem. This detailed resource details brute force and optimized approaches.
Problem Statement
Easy
Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.
Notice that the solution set must not contain duplicate triplets.
Write a function threeSum(nums: List[int]) -> List[List[int]].
Constraints
- •3 <= len(nums) <= 3000
- •-10^5 <= nums[i] <= 10^5
Examples
Example 1
Input
nums = [-1, 0, 1, 2, -1, -4]
Output
[[-1, -1, 2], [-1, 0, 1]]
Explanation
nums[0] + nums[1] + nums[2] = -1 + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = -1 + 2 + (-1) = 0. The distinct triplets are [-1,-1,2] and [-1,0,1].
Example 2
Input
nums = [0, 1, 1]
Output
[]
Explanation
No triplet sums to 0.
Example 3
Input
nums = [0, 0, 0]
Output
[[0, 0, 0]]
Explanation
The only possible triplet sums to 0.
Need a Hint?
Use two pointer variables starting at different bounds (e.g. left = 0, right = length - 1) and shrink the search window.
Edge Cases to Watch
- Empty list or null input variables
- Single item lists/arrays
- Extremely large input bounds causing integer or stack overflow
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