题解 | 山峰数组计数

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=2e5+10;

int n,P[N],sum[N];

void solve(){
	
	int area1,area2,area3;
	int res=0;
	for(int i=1,j=2;i<=n-2;i++){
		area1=sum[i]-sum[0];
		area2=sum[j]-sum[i];
		area3=sum[n]-sum[j];
		while(j+1<=n-1&&(area1>=area2||area3>=area2)){
			j++;
			area2=sum[j]-sum[i];
			area3=sum[n]-sum[j];
		}
		if((area1<area2)&&(area3<area2)){
			res+=n-j;
		}
	}
	cout<<res<<endl;
}

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>P[i];
		sum[i]=sum[i-1]+P[i];
	}
	
	solve();

    return 0;
}