#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<cmath>
#include<vector>
#include<stack>
#include<queue>
#include<set>
#include<map>
#include<unordered_map>
#define x first
#define y second
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
// #define int long long
using namespace std;
signed main(){
  int m,n;
  cin >> m >> n;
  vector<int>a(int(3e5 + 7));
  vector<pii>pos(int(3e5 + 7),mp(1e9,-1));
  for(int i = 0;i < m;i++){
    cin >> a[i];
    pos[a[i]].x = min(i,pos[a[i]].x);
    pos[a[i]].y = max(i,pos[a[i]].y);
  }
  stack<int>s;
  set<int>ss;
  for(int i = 0;i < m;i++){
    if(ss.count(a[i]) == 0){
      if(pos[a[i]].y == i){
        continue;
      }
      ss.insert(a[i]);
      s.push(a[i]);
    }else{
      if(s.top() != a[i]){
        cout << "-1";
        return 0;
      }else{
        s.pop();
        if(i != pos[a[i]].y){
          s.push(a[i]);
        }else{
          ss.erase(a[i]);
        }
      }
    }
  }
  int cnt = 0;
  for(int i = 0;i < m;i++){
    if(pos[a[i]].x == i){
      cnt++;
      // cout << a[i] << ' ' << pos[a[i]].x + 1 << ' ' << pos[a[i]].y + 1<< endl;
    }
  }
  cout << cnt << endl;
  for(int i = 0;i < m;i++){
    if(pos[a[i]].x == i){
      // cnt++;
      cout << a[i] << ' ' << pos[a[i]].x + 1 << ' ' << pos[a[i]].y + 1<< endl;
    }
  }
  return 0;
}