DP——Maximum Subarray

本文介绍了一种寻找数组中连续子列最大和的算法实现,通过动态规划思想,利用sum数组记录中间结果,并最终返回最大子列和。

问题描述:

在数组中找到连续的子列(包含至少一个数字),使其和最大。

解题思路:

声明一个sum数组,用来记录当前连续子列的最大和。key:如果当前元素加上sum[i-1],比本身的数值要小的话,则选取当前元素的数值作为sum[i]

源代码:

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        vector<int> sum;
        sum.push_back(nums[0]);
        for(int i=1;i<nums.size();i++)
        {
            if(nums[i]>sum[i-1]+nums[i]) sum.push_back(nums[i]);
            else sum.push_back(sum[i-1]+nums[i]);
        }
        int max=sum[0];
        for(int i=0;i<sum.size();i++)
            if(max<sum[i]) max=sum[i];
        return max;
    }
};
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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