Range Minimum Query Segment Tree c++ implementation

SegTree_RMQ_blog_1.cpp

#include<bits/stdc++.h>
using namespace std;
 
class SegmentTree{
	long long n;
	vector<long long>A,st;
	
	long long left(long long p)
	{
		return (p<<1);
	}
	
	long long right(long long p)
	{
		return (p<<1)+1;
	}
	
	void build(long long p,long long l,long long r)
	{
		if(l==r)
		st[p]=l;
		else
		{
			build(left(p),l,(l+r)/2);
			build(right(p),((l+r)/2)+1,r);
			long long li=st[left(p)];
			long long ri=st[right(p)];
			
			if(A[li]<A[ri])
			st[p]=li;
			else
			st[p]=ri;				
		}
	}
	
	long long rmq(long long p,long long l,long long r,long long i,long long j)
	{
		if(i>r || j<l)
		return -1;
		else if(l>=i && r<=j)
		return st[p];
		
		long long li=rmq(left(p),l,(l+r)/2,i,j);
		long long ri=rmq(right(p),((l+r)/2)+1,r,i,j);
		
		if(li==-1)
		return ri;
		else if(ri==-1)
		return li;
		else
		{
			if(A[li]<A[ri])
			return li;
			else
			return ri;
		}
	}
	
	public:
		SegmentTree(const vector<long long> &_A)
		{
			A=_A;
			n=(long long)(A.size());
			st.assign(4*n,0);
			build(1,0,n-1);
		}
		
		long long rmq(long long i,long long j)
		{
			return rmq(1,0,n-1,i,j);
		}
};

int main()
{
	long long a[]={2,1,7,5,4,6,4,3,5,4,9};
	vector<long long>v(a,a+11);
	SegmentTree st(v);
	cout<<"Range Minimun Query[L,R]=[1,8](index):"<<st.rmq(0,7)<<" value of min:"<<a[st.rmq(0,7)]<<"\n";
	cout<<"Range Minimun Query[L,R]=[9,11](index):"<<st.rmq(8,10)<<" value of min:"<<a[st.rmq(8,10)]<<"\n";
	return 0;
}