n=int(input()) ; arr=[int(i) for i in input().split()] ; dic=dict() ; c=0
for i in range(n):
x=arr[i]
if x not in dic: dic[x]=[i]
else:
dic[x].append(i)
arr2=[]
x=list(dic.keys())
x.sort()
for i in x:
z=dic[i]
if len(z)==1: arr2.append([i,0])
else:
d=z[1]-z[0]
for j in range(2,len(z)):
if z[j]-z[j-1]!=d:
break
else:arr2.append([i,d])
print(len(arr2))
for i in arr2:
print(*i)
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
ll m = 1000000007;
void solve() {
map<int,vector<int>> indexes;
int n;
cin >> n;
vector<int> a(n);
for(int i = 0; i < n; i++) {
cin >> a[i];
indexes[a[i]].push_back(i+1);
}
int cnt = 0;
vector<vector<int>> ans;
for(auto i = indexes.begin(); i !=indexes.end(); i++) {
vector<int> temp = i->second;
if(temp.size() == 1) {
cnt++;
ans.push_back({i->first, 0});
continue;
}
int diff = temp[1] - temp[0];
int flag = 0;
for(int j = 1; j < temp.size(); j++) {
if(temp[j] - temp[j-1] != diff) {
flag = 1;
break;
}
}
if(!flag) {
cnt++;
ans.push_back({i->first, diff});
}
}
cout << cnt << endl;
for(int i = 0; i < ans.size(); i++)
cout << ans[i][0] << " " << ans[i][1] << endl;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int tc = 1;
// cin >> tc;
for (int t = 1; t <= tc; t++)
{
// cout << "Case #" << t << ": ";
solve();
}
}
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