27C - Unordered Subsequence - CodeForces Solution

#include <bits/stdc++.h>
#define lli long long int
#define ii pair<lli,lli>
#define fi first
#define se second
using namespace std;
struct seg
{
	lli val,l,r;
};
int main ()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    int n; cin>>n;
    lli a[n+1];/////
    for (int i=1;i<=n;i++) cin>>a[i];/////////
    vector<seg>abc;//gadsgsad
    int cur=1;
    for (int i=2;i<=n;i++)
    {
    	if (a[i]!=a[i-1]) abc.push_back((seg){a[i-1],cur,i}), cur=i;
	}
	abc.push_back((seg){a[n],cur,n});
	if (abc.size()<3) return cout<<0,0;
	else for (int i=1;i<abc.size()-1;i++)
	{
		if (abc[i-1].val>abc[i].val && abc[i+1].val>abc[i].val)
		{
			return cout<<"3\n"<<abc[i-1].l<<" "<<abc[i].l<<" "<<abc[i+1].l,0;
		}
		else if (abc[i-1].val<abc[i].val && abc[i+1].val<abc[i].val)
		{
			return cout<<"3\n"<<abc[i-1].l<<" "<<abc[i].l<<" "<<abc[i+1].l,0;
		}
	}
	cout<<0;
}