leetcode 1043. Partition Array for Maximum Sum

本文详细解析了LeetCode上的1043题Partition Array for Maximum Sum的解题思路,通过动态规划方法,讲解如何将数组分割并替换为段内最大值以获得最大总和。

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leetcode 1043. Partition Array for Maximum Sum

题意:分割一个数组,保证分割的每个段最多K个数,将每个段的每个数换成当前段最大的那个数,求最终的最大值。

思路:简单DP。dp[i]表示分割完前i个数,最大值是多少。

j表示当前段的长度[1,K]。

假设我们知道[i-j,i]这一段的最大值curMax,那么dp[i]可以从dp[i-j]推过来。

 dp[i] = max(dp[i],(i>=K?dp[i-j]:0)+curMax*j);

curMax又可以通过遍历j的时候来更新。

class Solution {
public:
    int maxSumAfterPartitioning(vector<int>& A, int K) {
        int n = A.size();
        vector<int> dp(n,0);
        
        
        for(int i=0;i<A.size();i++)
        {
            int curMax = 0;
            for(int j=1;j<=K && i-j+1>=0;j++)
            {
                curMax = max(curMax,A[i-j+1]);
                dp[i] = max(dp[i],(i>=K?dp[i-j]:0)+curMax*j);
            }
        }
        return dp[n-1];
    }
};

 

Yousef has an array a of size n . He wants to partition the array into one or more contiguous segments such that each element ai belongs to exactly one segment. A partition is called cool if, for every segment bj , all elements in bj also appear in bj+1 (if it exists). That is, every element in a segment must also be present in the segment following it. For example, if a=[1,2,2,3,1,5] , a cool partition Yousef can make is b1=[1,2] , b2=[2,3,1,5] . This is a cool partition because every element in b1 (which are 1 and 2 ) also appears in b2 . In contrast, b1=[1,2,2] , b2=[3,1,5] is not a cool partition, since 2 appears in b1 but not in b2 . Note that after partitioning the array, you do not change the order of the segments. Also, note that if an element appears several times in some segment bj , it only needs to appear at least once in bj+1 . Your task is to help Yousef by finding the maximum number of segments that make a cool partition. Input The first line of the input contains integer t (1≤t≤104 ) — the number of test cases. The first line of each test case contains an integer n (1≤n≤2⋅105 ) — the size of the array. The second line of each test case contains n integers a1,a2,…,an (1≤ai≤n ) — the elements of the array. It is guaranteed that the sum of n over all test cases doesn't exceed 2⋅105 . Output For each test case, print one integer — the maximum number of segments that make a cool partition. Example InputCopy 8 6 1 2 2 3 1 5 8 1 2 1 3 2 1 3 2 5 5 4 3 2 1 10 5 8 7 5 8 5 7 8 10 9 3 1 2 2 9 3 3 1 4 3 2 4 1 2 6 4 5 4 5 6 4 8 1 2 1 2 1 2 1 2 OutputCopy 2 3 1 3 1 3 3 4 Note The first test case is explained in the statement. We can partition it into b1=[1,2] , b2=[2,3,1,5] . It can be shown there is no other partition with more segments. In the second test case, we can partition the array into b1=[1,2] , b2=[1,3,2] , b3=[1,3,2] . The maximum number of segments is 3 . In the third test case, the only partition we can make is b1=[5,4,3,2,1]
最新发布
06-09
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