#include <stdio.h>
#include <vector>
#define pii pair<int, int>
#define x first
#define y second
#define MAX 100005
using namespace std;

int n, m, a, b, v[MAX], pos[MAX], res[MAX], arb[2 * MAX], t = 1, cur = 1;
vector<pii> q[MAX];

int query(int node, int s, int d, int l, int r){
	if(l <= s && d <= r)
		return arb[node];
	if(r < s || d < l)
		return 0;
	return max(query(2 * node, s, (s + d) / 2, l, r), query(2 * node + 1, (s + d) / 2 + 1, d, l, r));
}

void update(int a, int b){
	a += t - 1;
	arb[a] = b;
	a >>= 1;
	while(a){
		arb[a] = max(arb[2 * a], arb[2 * a + 1]);
		a >>= 1;
	}
}

int main(){
	freopen("pq.in", "r", stdin);
	freopen("pq.out", "w", stdout);
	scanf("%d%d", &n, &m);
	while(t < n)
		t <<= 1;
	for(int i = 1; i <= n; ++i)
		scanf("%d", &v[i]);

	for(int i = 0; i < m; ++i){
		scanf("%d%d", &a, &b);
		q[b].push_back(make_pair(a, i));
	}

	for(int i = 1; i <= n; ++i){
		if(pos[v[i]])
			update(pos[v[i]], i - pos[v[i]]);
		pos[v[i]] = i;

		for(int j = 0; j < q[i].size(); ++j)
			res[q[i][j].y] = query(1, 1, n, q[i][j].x, i);
	}

	for(int i = 0; i < m; ++i)
		printf("%d\n", res[i] == 0 ? -1 : res[i]);
	return 0;
}