Codeforces Round #204 (Div. 2), problem: (B) Jeff and Periods

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization ("unroll-loops")

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define pii pair<int,int>
#define pli pair<long long int,int>
#define pbi pair<bool,int>
#define pob pop_back
#define all(a) a.begin(),a.end()
#define fio ios_base::sync_with_stdio(false); cin.tie(NULL);cout.tie(NULL);
#define i64 long long int
#define mem(x,y) memset(x,y,sizeof(x))
#define fill(arr,b) fill(arr, arr+sizeof(arr)/sizeof(arr[0]), b)
#define maxarr(n,arr,m) m=-1e9;for(int i=0;i<n;i++)if(arr[i]>m) m=arr[i];
#define read freopen("input.txt","r",stdin);
#define sortd(x,y) sort(x,y,greater<int>());
#define F first
#define S second

const int maxn = (i64)1e9+7;
const double pi = acos(-1.0);

//bool fne(const pii &a, const pii &b){return (a.F > b.F)||(a.F==b.F&&a.S>b.S);}
//bool sne(const pii &a, const pii &b){return (a.S < b.S)||(a.S==b.S&&a.F<b.F);}
//bool isprime(int n){for(int i=2;i*i<=n;i++){if(n%i==0)return false;}return true;}

int main(){
    //read;
    fio;
    int n;
    cin>>n;
    pii arr[n+3];
    for(int i=0;i<n;i++) {cin>>arr[i].F;arr[i].S=i;}
    sort(arr,arr+n);
    vector<pii>v;
    int diff=0,prev=-1;
    bool fg=true;
    for(int i=0;i+1<n;i++){
        if(arr[i].F==arr[i+1].F) {
            diff=arr[i+1].S-arr[i].S;
            if(prev==-1)prev=diff;
            else if(prev!=diff)fg=false;
        }
        else{
            if(fg)v.pb({arr[i].F,diff});
            diff=0;prev=-1;fg=true;
        }
    }
    if(fg)v.pb({arr[n-1].F,diff});
    int sz=v.size();
    cout<<sz<<endl;
    for(int i=0;i<sz;i++) cout<<v[i].F<<" "<<v[i].S<<endl;
    return 0;

}