#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

class UnionFind {
public:
  vector<int> parent;
  vector<int> _size;

  UnionFind(int n) {
    for (int i = 0; i < n; ++i) {
      parent.push_back(i);
      _size.push_back(1);
    }
  }

  int find(int x) {
    if (parent[x] == x) {
      return x;
    } else {
      return parent[x] = find(parent[x]);
    }
  }

  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) return;

    if (x > y) {
      parent[x] = y;
      _size[y] += _size[x];
    } else {
      parent[y] = x;
      _size[x] += _size[y];
    }
  }

  bool same(int x, int y) {
    return find(x) == find(y);
  }

  int size(int x) {
    return _size[find(x)];
  }
};

int T, R;

struct Command {
  int u;
  int v;

  Command(int u = -1, int v = -1) {
    this->u = u;
    this->v = v;
  }

  string to_str() {
    return to_string(u) + " " + to_string(v);
  }
};

class Adv2021 {
public:
  void run() {
    int N;
    int id = 1;
    int counter[101];
    memset(counter, 0, sizeof(counter));
    vector<int> started_at(5555, 9999);
    vector<int> skills[101];
    UnionFind uf(5555);
    vector<int> power(5555, 0);

    for (int t = 0; t < T; ++t) {
      cin >> N;
      vector<int> S(N);
      vector <Command> commands;

      for (int i = 0; i < N; ++i) {
        int s;
        cin >> s;
        S[i] = s;
        power[id] = s;
        skills[s].push_back(id);
        started_at[id] = t;
        int u = skills[s].back();
        int diff = 2;
        if (abs(s - 50) >= 25) diff = 3;
        if (abs(s - 50) >= 40) diff = 5;
        int max_time = -1;
        int min_time = 9999;
        int best_v = -1;

        for (int ns = max(0, s - diff); ns <= min(100, s + diff); ++ns) {
          if (skills[ns].empty()) continue;

          for (int v : skills[ns]) {
            int size = uf.size(u) + uf.size(v);
            int time = t - started_at[v];

            if (not uf.same(u, v) && size <= R && max_time < time) {
              max_time = time;
              best_v = v;
            }
          }
        }

        if (best_v != -1) {
          uf.unite(u, best_v);
          started_at[uf.find(u)] = min(started_at[u], started_at[best_v]);
          started_at[uf.find(best_v)] = min(started_at[u], started_at[best_v]);
          commands.push_back(Command(u, best_v));
        }

        counter[s]++;
        id++;
      }

      cout << commands.size() << endl;
      for (Command &cmd : commands) {
        cout << cmd.to_str() << endl;
      }
      cout << flush;
    }

    vector<bool> checked(5555, false);

    for (int i = 1; i < id; ++i) {
      int p = uf.find(i);
      if (checked[p]) continue;
      if (uf.size(p) == R) continue;
      checked[p] = true;

      fprintf(stderr, "x: %d, size: %d, st: %d\n", power[p], uf.size(p), started_at[p]);
    }

    for (int x = 0; x <= 100; ++x) {
      // fprintf(stderr, "x: %d, cnt: %d\n", x, counter[x]);
    }
  }
};

int main() {
  cin >> T >> R;

  Adv2021 solver;
  solver.run();

  return 0;
}