Three Sum Problem All Unique Triplets in DSA Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the goal of the Three Sum Problem?

To find all unique triplets in an array that add up to zero.

beginner

Why do we sort the array before solving the Three Sum Problem?

Sorting helps to avoid duplicates easily and allows using two pointers to find pairs efficiently.

intermediate

Explain the two-pointer technique used in the Three Sum Problem.

After fixing one number, use two pointers starting from the next element and the end of the array to find pairs that sum to the negative of the fixed number.

intermediate

How do you avoid duplicate triplets in the Three Sum Problem?

Skip over duplicate numbers for the fixed element and also skip duplicates when moving the two pointers.

intermediate

What is the time complexity of the common solution to the Three Sum Problem?

O(n^2), where n is the number of elements in the array.

What is the first step in solving the Three Sum Problem?

A Sort the array

B Use a hash map

C Reverse the array

D Remove duplicates

Sorting the array helps to efficiently find triplets and avoid duplicates.

In the two-pointer approach, what do the two pointers represent?

A The smallest and largest elements in the array

B Start and end of the array segment after the fixed element

C Random positions in the array

D Indices of duplicate elements

The two pointers start just after the fixed element and at the end of the array segment to find pairs summing to a target.

How do you handle duplicates for the fixed element in the Three Sum Problem?

A Use a hash set to store duplicates

B Include all duplicates

C Remove duplicates before processing

D Skip the fixed element if it is the same as the previous one

Skipping fixed elements that are the same as the previous avoids duplicate triplets.

What is the sum target for the two pointers after fixing one element?

A Negative of the fixed element

B Zero

C Sum of the fixed element and zero

D Double the fixed element

The two pointers look for two numbers that sum to the negative of the fixed element to make the total zero.

What is the overall time complexity of the common Three Sum solution?

A O(n^3)

B O(n log n)

C O(n^2)

D O(n)

The solution uses sorting O(n log n) and a nested loop with two pointers O(n^2), so overall O(n^2).

Describe the step-by-step approach to solve the Three Sum Problem with unique triplets.

Think about sorting, fixing one number, and searching pairs with two pointers.

Explain how to avoid duplicate triplets when solving the Three Sum Problem.

Focus on skipping duplicates at each step to ensure unique triplets.