#636 (Div. 3)C. Alternating Subsequence

제목 분석
Recall that the sequence b is a a subsequence of the sequence a if b can be derived from a by removing zero or more elements without changing the order of the remaining elements. For example, if a=[1,2,1,3,1,2,1], then possible subsequences are: [1,1,1,1], [3] and [1,2,1,3,1,2,1], but not [3,2,3] and [1,1,1,1,2]. You are given a sequence a consisting of n positive and negative elements (there is no zeros in the sequence). Your task is to choose maximum by size (length) alternating subsequence of the given sequence (i.e. the sign of each next element is the opposite from the sign of the current element, like positive-negative-positive and so on or negative-positive-negative and so on). Among all such subsequences, you have to choose one which has the maximum sum of elements. In other words, if the maximum length of alternating subsequence is k then your task is to find the maximum sum of elements of some alternating subsequence of length k. You have to answer t independent test cases.
Input
The first line of the input contains one integer t (1≤t≤104) — the number of test cases. Then t test cases follow. The first line of the test case contains one integer n (1≤n≤2⋅105) — the number of elements in a. The second line of the test case contains n integers a1,a2,…,an (−109≤ai≤109,ai≠0), where ai is the i-th element of a. It is guaranteed that the sum of n over all test cases does not exceed 2⋅105 (∑n≤2⋅105).
Output
For each test case, print the answer — the maximum sum of the maximum by size (length) alternating subsequence of a.
Example
input 4 5 1 2 3 -1 -2 4 -1 -2 -1 -3 10 -2 8 3 8 -4 -15 5 -2 -3 1 6 1 -1000000000 1 -1000000000 1 -1000000000 output 2 -1 6 -2999999997
Note
In the first test case of the example, one of the possible answers is [1,2,3–,−1–––,−2]. In the second test case of the example, one of the possible answers is [−1,−2,−1–––,−3]. In the third test case of the example, one of the possible answers is [−2–––,8,3,8–,−4–––,−15,5–,−2–––,−3,1–]. In the fourth test case of the example, one of the possible answers is [1–,−1000000000,1,-1000000000,1,−1000000000].
제목의 대의.
가장 긴 +-+-+-+-+-(+-교체만 가능)의 서열을 찾아서 가장 긴 서열의 최대치를 구합니다.
이 문제를 풀었는데 마지막에 해킹을 당했어요...
제목 분석
이 문제는 별로 할 말이 없는 것 같다. 바로 각 단락의 전체 양이나 전체 음의 서열 최대치를 가장 긴 서열의 수로 찾아내면 되고 쌍지침 알고리즘을 사용할 수 있다.
ac 코드

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define LL long long
using namespace std;
const int N=2e5+5;
int a[N];
bool check(int x,int y)
{
	if((x>0&&y>0)||(x<0&&y<0)) return true;
	else return false;
}
int main()
{
    int t;
	cin>>t;
	while(t--)
	{
		int n;
		cin>>n;
		for(int i=0;i<n;i++)
		cin>>a[i];
		
		int i=0,j=0;
		LL sum=0;     //     int
		while(i<n)
		{
			j=i;
			int num=a[j];
			while(j+1<n&&check(a[j],a[j+1]))//  a[j] a[j+1]    
			{//     j    ，            Hacked 
				num=max(num,a[j+1]);   //              
				j++;
			}
			sum+=num;  //        
			i=j+1;
		}
		cout<<sum<<endl;
	}
    return 0;
}