主席树和nth_element都WA了，求助

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
void read(int &x){
	char c=getchar();
	int k=1;
	while(c<'0'||c>'9') {if(c=='-') k=-1;c=getchar();}
	for(x=0;c>='0'&&c<='9';c=getchar())
	x=x*10+c-'0';
	x*=k;
}
const int N=100005;
int n,m,a[N],b[N],x,y,k,z;
int main(){
	read(n);
	for(int i=1;i<=n;i++){
		read(a[i]);
	}
	read(m);
	while(m--){
		read(x);read(y);read(k);
		for(int i=x;i<=y;++i){
			b[i-x+1]=a[i];
		}
		z=y-x+2;
		nth_element(b+1,b+z,b+k);
		printf("%d\n",b[k]);
	}
	return 0;
}