The Number of Products

题目链接：http://codeforces.com/contest/1215/problem/B

给你n长度的数组。分别求出任意长度连续区间内乘积为负数和正数的个数。

#include<iostream>
using namespace std;

const int MAXN = 2e5+5;
long long dp1[MAXN], dp2[MAXN]; //以i为结尾的，有dp1[i]个区间含有奇数个负数,dp2[i]个区间含有偶数个负数
long long a[MAXN];

int main(){
    int n;
    cin >> n;
    for(int i = 1; i <= n; ++i)
        cin >> a[i];
    dp1[1] = (int) (a[1] < 0), dp2[1] = 1-dp1[1];
    long long ans1 = dp1[1], ans2 = dp2[1];
    for(int i = 2; i <= n; ++i){
        if(a[i] < 0){
            dp1[i] = dp2[i-1]+1;
            dp2[i] = dp1[i-1];
        }
        else{
            dp1[i] = dp1[i-1];
            dp2[i] = dp2[i-1]+1;
        }
        ans1 += dp1[i];
        ans2 += dp2[i];
    }
    cout << ans1 << " " << ans2 << endl;
    return 0;
}