description: An important meeting is to be held and there are exactly n people invited. At any moment, any two people can step back and talk in private. The same two people can talk several (as many as they want) times per meeting.
  
  Each person has limited sociability. The sociability of the i-th person is a non-negative integer a_i. This means that after exactly a_i talks this person leaves the meeting (and does not talk to anyone else anymore). If a_i = 0, the i-th person leaves the meeting immediately after it starts.
  
  A meeting is considered most productive if the maximum possible number of talks took place during it.
  
  You are given an array of sociability a, determine which people should talk to each other so that the total number of talks is as large as possible.
  
  Input
  
  The first line contains an integer t (1 ≤ t ≤ 1000) — the number of test cases.
  
  The next 2t lines contain descriptions of the test cases.
  
  The first line of each test case description contains an integer n (2 ≤ n ≤ 2 ⋅ 10^5) —the number of people in the meeting. The second line consists of n space-separated integers a_1, a_2, ..., a_n (0 ≤ a_i ≤ 2 ⋅ 10^5) — the sociability parameters of all people. 
  
  It is guaranteed that the sum of n over all test cases does not exceed 2 ⋅ 10^5. It is also guaranteed that the sum of all a_i (over all test cases and all i) does not exceed 2 ⋅ 10^5.
  
  Output
  
  Print t answers to all test cases.
  
  On the first line of each answer print the number k — the maximum number of talks possible in a meeting.
  
  On each of the next k lines print two integers i and j (1 ≤ i, j ≤ n and i ≠ j) — the numbers of people who will have another talk.
  
  If there are several possible answers, you may print any of them.
  
  Example
  
  Input
  
  
  8
  2
  2 3
  3
  1 2 3
  4
  1 2 3 4
  3
  0 0 2
  2
  6 2
  3
  0 0 2
  5
  8 2 0 1 1
  5
  0 1 0 0 6
  
  
  Output
  
  
  2
  1 2
  1 2
  3
  1 3
  2 3
  2 3
  5
  1 3
  2 4
  2 4
  3 4
  3 4
  0
  2
  1 2
  1 2
  0
  4
  1 2
  1 5
  1 4
  1 2
  1
  5 2
solution: import java.io.DataInputStream;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.PriorityQueue;
  
  public class D28 {
      static class Pair {
          int idx;
          int val;
  
          public Pair(int idx, int val) {
              this.idx = idx;
              this.val = val;
          }
  
          @Override
          public String toString() {
              return this.idx + " " + this.val;
          }
      }
  
      /*
      *
  2
  2 3
  3
  1 2 3
  4
  1 2 3 4
  3
  0 0 2*/
      private static String solve(int n, PriorityQueue<Pair> pq) {
          StringBuilder ans = new StringBuilder();
          int count = 0;
          while (pq.size()>1) {
              Pair max = pq.poll();
              Pair min = pq.poll();
  
              ans.append(String.format("%d %d",max.idx,min.idx)).append("\n");
              max.val--;
              min.val--;
              if (min.val>0) pq.add(min);
              if (max.val>0) pq.add(max);
              count++;
          }
          return count + "\n" + ans.toString();
      }
  
      public static void main(String[] args)
              throws IOException {
          Scanner s = new Scanner();
          int t = 1;
          t = s.nextInt();
          StringBuilder ans = new StringBuilder();
          int count = 0;
          while (t-- > 0) {
              int n = s.nextInt();
              int a[] = new int[n];
              PriorityQueue<Pair> pq = new PriorityQueue<>((x, y) -> {
                  return y.val - x.val;
              });
              for (int i = 0; i < n; i++) {
                  int val = s.nextInt();
                  if(val>0) pq.offer(new Pair(i+1, val));
  
              }
              ans.append(solve(n,     pq));
          }
          System.out.println(ans.toString());
      }
  
      static class Scanner {
          final private int BUFFER_SIZE = 1 << 16;
          private DataInputStream din;
          private byte[] buffer;
          private int bufferPointer, bytesRead;
  
          public Scanner() {
              din = new DataInputStream(System.in);
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public Scanner(String file_name) throws IOException {
              din = new DataInputStream(
                      new FileInputStream(file_name));
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public String readLine() throws IOException {
              byte[] buf = new byte[64]; // line length
              int cnt = 0, c;
              while ((c = read()) != -1) {
                  if (c == '\n') {
                      if (cnt != 0) {
                          break;
                      } else {
                          continue;
                      }
                  }
                  buf[cnt++] = (byte) c;
              }
              return new String(buf, 0, cnt);
          }
  
          public int nextInt() throws IOException {
              int ret = 0;
              byte c = read();
              while (c <= ' ') {
                  c = read();
              }
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          public long nextLong() throws IOException {
              long ret = 0;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
              if (neg)
                  return -ret;
              return ret;
          }
  
          public double nextDouble() throws IOException {
              double ret = 0, div = 1;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
  
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
  
              if (c == '.') {
                  while ((c = read()) >= '0' && c <= '9') {
                      ret += (c - '0') / (div *= 10);
                  }
              }
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          private void fillBuffer() throws IOException {
              bytesRead = din.read(buffer, bufferPointer = 0,
                      BUFFER_SIZE);
              if (bytesRead == -1)
                  buffer[0] = -1;
          }
  
          private byte read() throws IOException {
              if (bufferPointer == bytesRead)
                  fillBuffer();
              return buffer[bufferPointer++];
          }
  
          public void close() throws IOException {
              if (din == null)
                  return;
              din.close();
          }
      }
  
      public static long norm(long a, long MOD) {
          return ((a % MOD) + MOD) % MOD;
      }
  
      public static long msub(long a, long b, long MOD) {
          return norm(norm(a, MOD) - norm(b, MOD), MOD);
  
      }
  
      public static long madd(long a, long b, long MOD) {
          return norm(norm(a, MOD) + norm(b, MOD), MOD);
  
      }
  
      public static long mMul(long a, long b, long MOD) {
          return norm(norm(a, MOD) * norm(b, MOD), MOD);
  
  
      }
  
      public static long mDiv(long a, long b, long MOD) {
          return norm(norm(a, MOD) / norm(b, MOD), MOD);
      }
  
      public static String formattedArray(int a[]) {
          StringBuilder res = new StringBuilder("");
          for (int e : a)
              res.append(e).append(" ");
          return res.toString().trim();
  
      }
  
  }
  