CF 1215 B The Number of Products(思维题)

Posted yokel062

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了CF 1215 B The Number of Products(思维题)相关的知识,希望对你有一定的参考价值。

链接:https://codeforces.com/contest/1215/problem/B

You are given a sequence a1,a2,,ana1,a2,…,an consisting of nn non-zero integers (i.e. ai0ai≠0).

You have to calculate two following values:

  1. the number of pairs of indices (l,r)(l,r) (lr)(l≤r) such that alal+1ar1aral⋅al+1…ar−1⋅ar is negative;
  2. the number of pairs of indices (l,r)(l,r) (lr)(l≤r) such that alal+1ar1aral⋅al+1…ar−1⋅ar is positive;
Input

The first line contains one integer n(1n2105)(1≤n≤2⋅105) — the number of elements in the sequence.

The second line contains nn integers a1,a2,,ana1,a2,…,an (109ai109;ai0)(−109≤ai≤109;ai≠0) — the elements of the sequence.

Output

Print two integers — the number of subsegments with negative product and the number of subsegments with positive product, respectively.

 

题意:求乘积为负数和正数的子段个数(没有0)

题解:正数0,负数1,统计前缀和(就是求前缀和奇偶),再从头扫一遍,维护2个桶前缀和为奇数的个数和前缀和为偶数的个数。

技术图片
#include <bits/stdc++.h>
using namespace std;
 
const int maxn=2e5+5;
int n;
int a[maxn], sum[maxn], cnt[2];
long long pos, neg;
 
int main()
{
    ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    cin>>n;
    for(int i=1; i<=n; i++)
    {
        cin>>a[i];
        if(a[i]>0) a[i]=0;
        else a[i]=1;
    }
    for(int i=1; i<=n; i++)
        sum[i]=sum[i-1]+a[i];
    for(int i=1; i<=n; i++)
        sum[i]=sum[i]%2;
    cnt[0]++;                 //注意cnt0初始化为1,表示区间长度为1的那个
    for(int i=1; i<=n; i++)
    {
        if(sum[i]){
            pos+=cnt[1];
            neg+=cnt[0];
        }
        else{
            pos+=cnt[0];
            neg+=cnt[1];
        }
        cnt[sum[i]]++;
    }
    cout<<neg<<" "<<pos;
    return 0;
}
View Code

 

以上是关于CF 1215 B The Number of Products(思维题)的主要内容,如果未能解决你的问题,请参考以下文章

数学CF27E Number With The Given Amount Of Divisors

CF1175F The Number of Subpermutations

文文殿下CF1175F The Number of Subpermutations

CF724G. Xor-matic Number of the Graph

CF724G Xor-matic Number of the Graph

CF.724G.Xor-matic Number of the Graph(线性基)