Leetcode 740. Delete and Earn

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 numsi and delete it to earn numsi points. Afterwards, you must delete every element equal to numsi - 1 and every element equal to numsi + 1.

Return the maximum number of points you can earn by applying the above operation some number of times.

Algorithm

Dynamics Programming (DP). F(n) = max(F(n-1), F(n-2)) {if numsn exists} else F(n) = F(n-1).

Code

class Solution:
    def deleteAndEarn(self, nums: List[int]) -> int:
        max_value = 0
        for num in nums:
            if max_value < num:
                max_value = num

        flag = [0] * (max_value + 1)
        for num in nums:
            flag[num] += 1
        
        ans = [0] * (max_value + 1)
        ans[1] = flag[1]
        for i in range(2, max_value+1):
            ans[i] = ans[i-1]
            if i > 1 and flag[i] and ans[i] < ans[i-2] + i * flag[i]:
                ans[i] = ans[i-2] + i * flag[i]
        
        return max(ans[max_value], ans[max_value-1])