#include <cstdio>
#include <algorithm>
#include <map>
#define maxn 500010
const int inf = 0x3f3f3f3f;
inline int min(int a, int b) {return a < b ? a : b;}int a[maxn], pre[maxn], nxt[maxn];
std::map<int, int> mp;
struct Query {int l, r, id;inline bool operator < (const Query &rhs) const {return l < rhs.l;}
} Q[maxn];
int ans[maxn];int V[maxn << 2];
inline void update(int rt) {V[rt] = min(V[rt << 1], V[rt << 1 | 1]);
}
void build(int rt, int l, int r) {if (l == r) {if (pre[l]) V[rt] = l - pre[l];else V[rt] = inf;return ;}int mid = l + r >> 1;build(rt << 1, l, mid);build(rt << 1 | 1, mid + 1, r);update(rt);
}
void modify(int rt, int l, int r, int p) {if (l == r) {V[rt] = inf;return ;}int mid = l + r >> 1;if (p <= mid) modify(rt << 1, l, mid, p);else modify(rt << 1 | 1, mid + 1, r, p);update(rt);
}
int query(int rt, int l, int r, int L, int R) {if (L <= l && R >= r) return V[rt];int mid = l + r >> 1, ans = inf;if (L <= mid) ans = query(rt << 1, l, mid, L, R);if (R > mid) ans = min(ans, query(rt << 1 | 1, mid + 1, r, L, R));return ans;
}int n, m;
int main() {scanf("%d%d", &n, &m);for (int i = 1; i <= n; i++) {scanf("%d", a + i);if (mp.count(a[i])) pre[i] = mp[a[i]], nxt[mp[a[i]]] = i, mp[a[i]] = i;else pre[i] = 0, mp[a[i]] = i;}for (int i = 1; i <= m; i++) {scanf("%d%d", &Q[i].l, &Q[i].r);Q[i].id = i;}std::sort(Q + 1, Q + m + 1);build(1, 1, n);int last = 1;for (int i = 1; i <= m; i++) {int l = Q[i].l;for (; last < l; last++) {if (nxt[last] >= l) modify(1, 1, n, nxt[last]);}ans[Q[i].id] = query(1, 1, n, l, Q[i].r);}for (int i = 1; i <= m; i++) if (ans[i] != inf) printf("%d\n", ans[i]);else puts("-1");return 0;
}