#include <iostream>

 #include <vector>

 #include <cstdio>

 #include <cstring>

 #include <algorithm>

 #include <cmath>

 #include <map>

 #include <set>

 #include <string>

 #include <queue>

 #include <stack>

 #include <bitset>

 using namespace std;

 #define pb(x) push_back(x)

 #define ll long long

 #define mk(x, y) make_pair(x, y)

 #define lson l, m, rt<<1

 #define mem(a) memset(a, 0, sizeof(a))

 #define rson m+1, r, rt<<1|1

 #define mem1(a) memset(a, -1, sizeof(a))

 #define mem2(a) memset(a, 0x3f, sizeof(a))

 #define rep(i, n, a) for(int i = a; i<n; i++)

 #define fi first

 #define se second

 typedef pair<int, int> pll;

 const double PI = acos(-1.0);

 const double eps = 1e-;

 const int mod = 1e9+;

 const int inf = ;

 const int dir[][] = { {-, }, {, }, {, -}, {, } };

 const int maxn = 5e5+;

 int minn[maxn<<], a[maxn], ans1[maxn], ans;

 struct node

 {

     int l, r, id;

     bool operator < (node a)const

     {

         if(r == a.r)

             id<a.id;

         return r<a.r;

     }

 }q[maxn];

 map <int, int> mp;

 void pushUp(int rt) {

     minn[rt] = min(minn[rt<<], minn[rt<<|]);

 }

 void update(int p, int val, int l, int r, int rt) {

     if(l == r) {

         minn[rt] = val;

         return ;

     }

     int m = l+r>>;

     if(p<=m)

         update(p, val, lson);

     else

         update(p, val, rson);

     pushUp(rt);

 }

 void query(int L, int R, int l, int r, int rt) {

     if(L<=l&&R>=r) {

         ans = min(ans, minn[rt]);

         return ;

     }

     int m = l+r>>;

     if(L<=m)

         query(L, R, lson);

     if(R>m)

         query(L, R, rson);

 }

 int main()

 {

     int n, m;

     cin>>n>>m;

     for(int i = ; i<=n; i++)

         scanf("%d", &a[i]);

     for(int i = ; i<m; i++) {

         scanf("%d%d", &q[i].l, &q[i].r);

         q[i].id = i;

     }

     sort(q, q+m);

     int pos = ;

     mem2(minn);

     for(int i = ; i<=n; i++) {

         if(mp[a[i]]) {

             update(mp[a[i]], i-mp[a[i]], , n, );

         }

         mp[a[i]] = i;

         while(i == q[pos].r) {

             ans = inf;

             query(q[pos].l, i, , n, );

             if(ans == inf)

                 ans = -;

             ans1[q[pos].id] = ans;

             pos++;

         }

     }

     for(int i = ; i<m; i++)

         cout<<ans1[i]<<" ";

     return ;

 }