Last Stone Weight

Last Stone Weight is a Easy Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Heap (Priority Queue) Patterns pattern, in the Top K Elements (Selection/Frequency) subpattern.

Problem statement

You are given an array of integers stones where stones[i] is the weight of the ith stone.

We are playing a game with the stones. On each turn, we choose the heaviest two stones and smash them together. Suppose the heaviest two stones have weights x and y with x <= y. The result of this smash is:

- If x == y, both stones are destroyed, and

- If x != y, the stone of weight x is destroyed, and the stone of weight y has new weight y - x.

At the end of the game, there is at most one stone left.

Return the weight of the last remaining stone. If there are no stones left, return 0.

Example 1:

Input: stones = [2,7,4,1,8,1] Output: 1 Explanation: We combine 7 and 8 to get 1 so the array converts to [2,4,1,1,1] then, we combine 2 and 4 to get 2 so the array converts to [2,1,1,1] then, we combine 2 and 1 to get 1 so the array converts to [1,1,1] then, we combine 1 and 1 to get 0 so the array converts to [1] then that's the value of the last stone.

Example 2:

Input: stones = [1] Output: 1

Constraints:

- 1 <= stones.length <= 30

- 1 <= stones[i] <= 1000

Topics and companies

Topics: Array, Heap (Priority Queue).

Reported in interviews at Amazon.

How to practise Last Stone Weight on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(nlogn) time and O(n) space.

Open Last Stone Weight in the code editor, or read the Last Stone Weight editorial for a worked solution with its approach and complexity analysis.

Where Last Stone Weight sits in the DSA pattern sheet

• Heap (Priority Queue) Patterns pattern guide
• Top K Elements (Selection/Frequency) subpattern
• The full DSA patterns sheet
• All coding practice problems

Problems related to Last Stone Weight

Other problems that use the same Top K Elements (Selection/Frequency) and Heap (Priority Queue) Patterns techniques:

• K Closest Points to Origin — Medium, same subpattern
• Kth Largest Element in an Array — Medium, same subpattern
• Kth Largest Element in a Stream — Easy, same subpattern
• Relative Ranks — Easy, same subpattern
• Sort Characters By Frequency — Medium, same subpattern
• Take Gifts From the Richest Pile — Easy, same subpattern