740. Delete and Earn

Medium
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.
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.
Constraints:
  • 1 <= nums.length <= 2 * 104
  • 1 <= nums[i] <= 104

解題

這題 DP 的技巧和 198. House Robber 差不多。
Runtime: 7 ms, faster than 95.31%
Memory Usage: 5.9 MB, less than 39.58%
func deleteAndEarn(nums []int) int {
sum := make([]int, 10001)
maxNum := 0
​
for _, num := range nums {
sum[num] += num
if num > maxNum {
maxNum = num
}
}
​
dp := make([]int, 2)
dp[0] = 0
dp[1] = sum[1]
​
for i:=2; i<=maxNum; i++ {
dp = append(dp, max(dp[i - 1], dp[i - 2] + sum[i]))
}
​
return dp[maxNum]
}
​
func max(a, b int) int {
if a > b { return a }
return b
}