到底有什么问题啊

实在看不出来编译问题，求助dalao

#include<bits/stdc++.h>
using namespace std;
const int N=1e9;
int n,q,a[N],ans[N];
int main(){
	cin>>n>>q;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		if(i%2==0)ans[i]=ans[i-1]+a[i]-a[i-1];
		else ans[i]=ans[i-1];
	}
	while(q--){
		int r,l,time=0;
		cin>>r>>l;
		int first=lower_bound(a+1,a+1+n,r)-a;
		int end=upper_bound(a+1,a+1+n,l)-a-1;
		if(first%2==1)time+=a[first]-r;
		if(end%2==0)time+=l-a[end];
		cout<<ans[l]-ans[r]+time; 
	}
	return 0;
}