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740. Delete and Earn

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Pick numbers to maximize their sum, but taking value v deletes every v-1 and v+1. Reduces to House Robber on a value-indexed point array.

By Sam K., Founder, InterviewChamp.AI · Last verified

Problem

You are given an integer array nums. You want to maximize the number of points you get by performing the following operation any number of times: Pick any nums[i] and delete it to earn nums[i] points. Afterwards, you must delete every element equal to nums[i] - 1 and every element equal to nums[i] + 1. Return the maximum number of points you can earn by applying the above operation some number of times.

Constraints

  • 1 <= nums.length <= 2 * 10^4
  • 1 <= nums[i] <= 10^4

Examples

Example 1

Input
nums = [3,4,2]
Output
6

Explanation: You can perform the following operations: Delete 4 to earn 4 points. Consequently, 3 is also deleted. nums = [2]. Delete 2 to earn 2 points. nums = []. You earn a total of 6 points.

Example 2

Input
nums = [2,2,3,3,3,4]
Output
9

Explanation: You can perform the following operations: Delete a 3 to earn 3 points. All 2's and 4's are also deleted. nums = [3,3]. Delete a 3 again to earn 3 points. nums = [3]. Delete a 3 once more to earn 3 points. nums = []. You earn a total of 9 points.

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Output

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Hints

Progressive — try the first before opening the next.

Hint 1

Sum points by value. If you take any copy of v you take all copies (and forfeit v-1 and v+1).

Hint 2

Build points[v] = v * count(v). Now choose a subset of values with no two adjacent values v, v+1.

Hint 3

That is exactly House Robber on the points array indexed by value.

Solution approach

Reveal approach

Convert the multiset into a value-indexed point array. Let max_v = max(nums). Build points[0..max_v] where points[v] = v * count(v). Picking any copy of value v earns points[v] total and forbids v-1 and v+1. The problem reduces to: pick a subset of indices in points[] with no two adjacent, maximizing sum — exactly House Robber. Run the standard two-variable DP: prev2 = 0, prev1 = points[0]; for v in 1..max_v compute curr = max(prev1, prev2 + points[v]) and shift. Return prev1. O(N + V) where V is the max value.

Complexity

Time
O(N + V)
Space
O(V)

Related patterns

  • dynamic-programming
  • bucket
  • house-robber

Related problems

Asked at

Companies reported asking this problem (sourced from public Glassdoor, Blind, and Levels.fyi interview posts).

  • Amazon
  • Google

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