/**
 * Author      : Dipu Kumar Mohanto
 *               CSE, BRUR.
 * Problem     : D. Closest Equals
 * Category    : Data Structures Variations
 * 
 * Verdict     : Accepted
**/

Author            : Dipu Kumar Mohanto 
                    CSE, Batch - 6
                    BRUR.
Problem Statement : DCP-60: Holloween Party
Source            : Devskill
Category          : Graph Theory
Algorithm         : Sorting Queries
Verdict           : Accepted
 
#include "bits/stdc++.h"
 
using namespace std;
 
static const int maxn = 6e5 + 5;
static const int inf  = 1e7 + 7;
 
struct node
{
	int l, p;
	node(int l = 0, int p = 0) : l(l), p(p) {}
};
 
int arr[maxn];
map <int, int> mapper;
vector <node> allquery[maxn];
int ans[maxn];
int n, q;
 
int tree[maxn << 2];
 
inline void update(int node, int a, int b, int pos, int val)
{
	if (a > b || a > pos || b < pos) return;
	if (a >= pos && b <= pos)
	{
		tree[node] = min(tree[node], val);
		return;
	}
	int lft = node << 1;
	int rgt = lft | 1;
	int mid = (a + b) >> 1;
	update(lft, a, mid, pos, val);
	update(rgt, mid+1, b, pos, val);
	tree[node] = min(tree[lft], tree[rgt]);
} 
 
inline int query(int node, int a, int b, int i, int j)
{
	if (a > b || a > j || b < i) return inf;
	if (a >= i && b <= j) return tree[node];
	int lft = node << 1;
	int rgt = lft | 1;
	int mid = (a + b) >> 1;
	int p = query(lft, a, mid, i, j);
	int q = query(rgt, mid + 1, b, i, j);
	return min(p, q);
}
 
int main()
{
	scanf("%d %d", &n, &q);
	for (int i = 1; i <= n; i++) scanf("%d", &arr[i]);
	for (int i = 1; i <= q; i++)
	{
		int l, r;
		scanf("%d %d", &l, &r);
		allquery[r].emplace_back(l, i);
	}
	fill(begin(tree), end(tree), inf);
	for (int i = 1; i <= n; i++)
	{
		if (mapper.find(arr[i]) != mapper.end()) 
		{
			int pos = mapper[ arr[i] ];
			int val = i - pos;
			update(1, 1, n, pos, val);
		}
		mapper[ arr[i] ] = i;
		for (node it : allquery[i]) ans[it.p] = query(1, 1, n, it.l, i);  
	}
	for (int i = 1; i <= q; i++) printf("%d\n", ans[i] == inf ? -1 : ans[i]);
}