题意: 找到最长的+ - + - + - + - + -(即正负交替即可)的序列,并求其和的max。
思路: 利用双指针算法找到每一段全正或全负的子序列最大值作为最长序列的数即可。
代码实现:
#include<bits/stdc++.h>
#define endl '\n'
#define null NULL
#define ll long long
#define int long long
#define pii pair<int, int>
#define lowbit(x) (x &(-x))
#define ls(x) x<<1
#define rs(x) (x<<1+1)
#define me(ar) memset(ar, 0, sizeof ar)
#define mem(ar,num) memset(ar, num, sizeof ar)
#define rp(i, n) for(int i = 0, i < n; i ++)
#define rep(i, a, n) for(int i = a; i <= n; i ++)
#define pre(i, n, a) for(int i = n; i >= a; i --)
#define IOS ios::sync_with_stdio(0); cin.tie(0);cout.tie(0);
const int way[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
using namespace std;
const int inf = 0x7fffffff;
const double PI = acos(-1.0);
const double eps = 1e-6;
const ll mod = 1e9 + 7;
const int N = 2e5 + 5;
int t, n, a[N];
bool check(int x,int y)
{
if((x > 0 && y > 0)||(x < 0 && y < 0)) return 1;
return 0;
}
signed main()
{
IOS;
cin >> t;
while(t --){
cin >> n;
for(int i = 0; i < n; i ++) cin >> a[i];
int l = 0, r = 0, sum = 0;
while(l < n){
r = l;
int tmp = a[r];
while(r + 1 < n && check(a[r], a[r + 1]))
tmp = max(tmp, a[++ r]);
sum += tmp;
l = r + 1;
}
cout << sum << endl;
}
return 0;
}