#include <bits/stdc++.h>

using namespace std;

#define V vector

#define rmin(a, b) a = min(a, b)
#define rmax(a, b) a = max(a, b)

#define rep(i, lim) for (size_t i = 0; i < (lim); i++)
#define nrep(i, s, lim) for (size_t i = s; i < (lim); i++)

#define repv(i, v) for (auto &i : (v))
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
#define sortv(v) sort(v.begin(), v.end())
#define all(v) (v).begin(), (v).end()

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;

using ll = long long;

using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vvvvl = vector<vvvl>;

template<class v>
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
    os << vec[0];
    for (size_t i = 1; i < vec.size(); i++) {
        os << ' ' << vec[i];
    }
    os << '\n';
    return os;
}

template<class v>
auto operator>>(istream &is, vector<v> &vec)->istream& {
    for (auto &i : vec) {
        is >> i;
    }
    return is;
}

template<class v>
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
    for (auto &i : vec) {
        os << i[0];
        for (size_t j = 1; j < i.size(); j++) {
            os << ' ' << i[j];
        }
        os << '\n';
    }
    return os;
}

template<class v>
auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
    for (auto &i : vec) {
        for (auto &j : i) {
            is >> j;
        }
    }
    return is;
}

const int inf = INT32_MAX >> 1;

int closepower2(int n)
{
	return n == 1 ? 1 : 1 << (sizeof(n) * 8 - __builtin_clz(n - 1));
}

int nextpower2(int n)
{
	return n == 1 ? 1 : sizeof(n) * 8 - __builtin_clz(n - 1);
}

class segtree_min {
	struct segnode {
		int content;
		int left, right;

		segnode(): content(inf), left(0), right(0) {}
		segnode(int content): content(content), left(0), right(0) {}
		segnode(int content, int left, int right):
			content(content), left(left), right(right) {}

		int getcontent() const {
		    return content == inf ? -1 : content;
		}
	};

	vector<segnode> nodes;
	vector<int> roots;
	size_t alloc;
	int n;

	int create_leaf(long long v) {
		new (&nodes[alloc]) segnode(v);
		alloc++;
		return alloc - 1;
	}

	int update_node(int l, int r) {
		new (&nodes[alloc]) segnode(min(nodes[l].content, nodes[r].content), l, r);
		alloc++;
		return alloc - 1;
	}

	int _update(int i, int l, int r, int f, long long v) {
		if (l > f || r < f) {
			return i;
		}

		if (l == f && r == f) {
			int now = create_leaf(v);
			return now;
		}

		int mid = (l + r) / 2;
		int left = _update(nodes[i].left, l, mid, f, v);
		int right = _update(nodes[i].right, mid + 1, r, f, v);

		if (nodes[i].left == left && nodes[i].right == right) {
			return i;
		}

		if (nodes[i].left != left) {
			return update_node(left, nodes[i].right);
		}
		return update_node(nodes[i].left, right);
	}

	long long search(int i, int l, int r, int ql, int qr) {
		if (l > qr || r < ql) {
			return inf;
		}

		if (l >= ql && r <= qr) {
			return nodes[i].content;
		}

		int m = (l + r) / 2;
		return min(search(nodes[i].left, l, m, ql, qr), search(nodes[i].right, m + 1, r, ql, qr));
	}

	public:
	segtree_min() = delete;

	segtree_min(size_t n): nodes(closepower2(n) * 2 + nextpower2(n) * closepower2(n) + closepower2(n)),
	                       roots({0}), alloc(closepower2(n) * 2 - 1), n(closepower2(n) - 1) {
		for (size_t i = 0; i < closepower2(n) - 1; i++) {
			new (&nodes[i]) segnode(inf, i * 2 + 1, i * 2 + 2);
		}
	}

	void update(int i, long long v) {
		int root = _update(roots.back(), 0, n, i, v);
		roots.push_back(root);
	}

	long long query(int l, int r) {
		int root = roots[r];
		// int root = roots.back();
		l--, r--;
		return search(root, 0, n, l, r);
	}

	void print() {
		int root = roots.back();
		queue<int> q;
		q.push(root);
		while (!q.empty()) {
			int p = q.front();
			q.pop();
			if (nodes[p].left != 0) {
				q.push(nodes[p].left);
				q.push(nodes[p].right);
			}
			cout << nodes[p].getcontent() << ' ';
		}
		cout << '\n';
	}

	void print_full() {
		int root = roots.back();
		queue<int> q;
		q.push(root);
		while (!q.empty()) {
			int p = q.front();
			q.pop();
			if (nodes[p].left != 0) {
				q.push(nodes[p].left);
				q.push(nodes[p].right);
			}
			cout << p << ": " << nodes[p].getcontent() << ' ' << nodes[p].left << ' ' << nodes[p].right << '\n';
		}
	}

	void print_roots() {
		for (auto i : roots) {
			cout << i << ' ';
		}
		cout << '\n';
	}

	void print_all_ver() {
		for (auto i : roots) {
			queue<long long> q;
			q.push(i);
			while (!q.empty()) {
				int p = q.front();
				q.pop();
				if (nodes[p].left != 0) {
					q.push(nodes[p].left);
					q.push(nodes[p].right);
				}
				cout << nodes[p].getcontent() << ' ';
			}
			cout << '\n';
		}
	}
};

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int n, m;
	cin >> n >> m;
	vector<long long> nums(n);
	for (auto &i : nums) {
		cin >> i;
	}

	segtree_min seg(n);
	map<int, int> dis;

	for (size_t i = 0; i < n; i++) {
		long long now = inf;
		if (dis.find(nums[i]) != dis.end()) {
			now = i - dis[nums[i]];
			seg.update(dis[nums[i]], now);
		} else {
			seg.update(i, inf);
		}
		dis[nums[i]] = i;
	}

	while (m--) {	
		int l, r;
		cin >> l >> r;
		long long ans = seg.query(l, r);
		cout << (ans == inf ? -1 : ans) << '\n';
	}
}