LeetCode 740. Delete and Earn

原题链接在这里:https://leetcode.com/problems/delete-and-earn/

题目:

Given an array nums of integers, you can perform operations on the array.

In each operation, you pick any nums[i] and delete it to earn nums[i] points. After, you must delete every element equal to nums[i] - 1 or nums[i] + 1.

You start with 0 points. Return the maximum number of points you can earn by applying such operations.

Example 1:

Input: nums = [3, 4, 2]
Output: 6
Explanation: 
Delete 4 to earn 4 points, consequently 3 is also deleted.
Then, delete 2 to earn 2 points. 6 total points are earned.

Example 2:

Input: nums = [2, 2, 3, 3, 3, 4]
Output: 9
Explanation: 
Delete 3 to earn 3 points, deleting both 2's and the 4.
Then, delete 3 again to earn 3 points, and 3 again to earn 3 points.
9 total points are earned.

Note:

  • The length of nums is at most 20000.
  • Each element nums[i] is an integer in the range [1, 10000].

题解:

Sort the numbers into bucket. 

If you take the current bucket, you can't take next to it.

include[i] denotes max points earned by taking bucket i, include[i] = exclude[i-1] + i*buckets[i].

exclude[i] denotes max points earned by skipping bucket i, exclude[i] = Math.max(include[i-1], exclude[i-1]).

Time Complexity: O(nums.length + range). range = 10000.

Space: O(range).

AC Java: 

 1 class Solution {
 2     public int deleteAndEarn(int[] nums) {
 3         if(nums == null || nums.length == 0){
 4             return 0;
 5         }
 6         
 7         int n = 10001;
 8         int [] buckets = new int[n];
 9         for(int num : nums){
10             buckets[num]++;
11         }
12         
13         int in = 0;
14         int ex = 0;
15         for(int i = 0; i<n; i++){
16             int inclusive = ex + i*buckets[i];
17             int exclusive = Math.max(in, ex);
18             in = inclusive;
19             ex = exclusive;
20         }
21         
22         return Math.max(in, ex);
23     }
24 }

类似House Robber.

posted @ 2019-09-03 11:37  Dylan_Java_NYC  阅读(407)  评论(0编辑  收藏  举报