#include <fstream>
#include <algorithm>
#define x first
#define y second
using namespace std;
ifstream f("pq.in");
ofstream g("pq.out");
int n,t,i,step,xi,a,b,nr,v[1<<17];
pair <int,int> V[1<<17];
struct cmp
{
    bool operator () (pair <int,int> a,pair <int,int> b)
    {
        return a.y-a.x<b.y-b.x;
    }
};
int main()
{
    f>>n>>t;
    for(i=1;i<=n;++i)
    {
        f>>xi;
        if(v[xi]) V[++nr]={v[xi],i};
        v[xi]=i;
    }
    sort(V+1,V+nr+1,cmp());
    while(t--)
    {
        f>>a>>b;
        for(i=0,step=1<<17;step;step>>=1)
            if(i+step<=nr&&V[i+step].y-V[i+step].x<=b-a) i+=step;
        if(!i) g<<"-1\n";
        while(i)
        {
            if(V[i].x>=a&&V[i].y<=b)
            {
                g<<V[i].y-V[i].x<<'\n';
                break;
            }
            --i;
            if(!i) g<<"-1\n";
        }
    }
    return 0;
}