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
}