description: Consider a sequence of integers a_1, a_2, …, a_n. In one move, you can select any element of the sequence and delete it. After an element is deleted, all elements to the right are shifted to the left by 1 position, so there are no empty spaces in the sequence. So after you make a move, the sequence's length decreases by 1. The indices of the elements after the move are recalculated.
  
  E. g. let the sequence be a=[3, 2, 2, 1, 5]. Let's select the element a_3=2 in a move. Then after the move the sequence will be equal to a=[3, 2, 1, 5], so the 3-rd element of the new sequence will be a_3=1 and the 4-th element will be a_4=5.
  
  You are given a sequence a_1, a_2, …, a_n and a number k. You need to find the minimum number of moves you have to make so that in the resulting sequence there will be at least k elements that are equal to their indices, i. e. the resulting sequence b_1, b_2, …, b_m will contain at least k indices i such that b_i = i.
  
  Input
  
  The first line contains one integer t (1 ≤ t ≤ 100) — the number of test cases. Then t test cases follow.
  
  Each test case consists of two consecutive lines. The first line contains two integers n and k (1 ≤ k ≤ n ≤ 2000). The second line contains a sequence of integers a_1, a_2, …, a_n (1 ≤ a_i ≤ n). The numbers in the sequence are not necessarily different.
  
  It is guaranteed that the sum of n over all test cases doesn't exceed 2000.
  
  Output
  
  For each test case output in a single line:
  
    * -1 if there's no desired move sequence; 
    * otherwise, the integer x (0 ≤ x ≤ n) — the minimum number of the moves to be made so that the resulting sequence will contain at least k elements that are equal to their indices. 
  
  Example
  
  Input
  
  
  4
  7 6
  1 1 2 3 4 5 6
  5 2
  5 1 3 2 3
  5 2
  5 5 5 5 4
  8 4
  1 2 3 3 2 2 5 5
  
  
  Output
  
  
  1
  2
  -1
  2
  
  Note
  
  In the first test case the sequence doesn't satisfy the desired condition, but it can be provided by deleting the first element, hence the sequence will be [1, 2, 3, 4, 5, 6] and 6 elements will be equal to their indices.
  
  In the second test case there are two ways to get the desired result in 2 moves: the first one is to delete the 1-st and the 3-rd elements so that the sequence will be [1, 2, 3] and have 3 elements equal to their indices; the second way is to delete the 2-nd and the 3-rd elements to get the sequence [5, 2, 3] with 2 desired elements.
solution: /**
   * author: derrick20
   * created: 8/3/21 11:35 PM
   */
  import java.io.*;
  import java.util.*;
  import static java.lang.Math.*;
  
  public class E_FixedPoints {
      static FastScanner sc = new FastScanner();
      static PrintWriter out = new PrintWriter(System.out);
      
      public static void main(String[] args) {
          int T = sc.nextInt();
          while (T-->0) {
              int N = sc.nextInt();
              int K = sc.nextInt();
              int[] a = new int[N + 1];
              Arrays.setAll(a, i -> i == 0 ? 0 : sc.nextInt() - i);
              int[][] dp = new int[N + 1][N + 1];
              int minMoves = -1;
              for (int k = 0; k <= N; k++) {
                  for (int i = 1; i <= N; i++) {
                      dp[k][i] = dp[k][i - 1] + (k + a[i] == 0 ? 1 : 0);
                      if (k > 0) {
                          dp[k][i] = max(dp[k][i], dp[k - 1][i - 1]);
                      }
                  }
                  if (dp[k][N] >= K) {
                      minMoves = k;
                      break;
                  }
              }
              out.println(minMoves);
          }
          out.close();
      }
  
      static class FastScanner {
          private int BS = 1 << 16;
          private char NC = (char) 0;
          private byte[] buf = new byte[BS];
          private int bId = 0, size = 0;
          private char c = NC;
          private double cnt = 1;
          private BufferedInputStream in;
      
          public FastScanner() {
              in = new BufferedInputStream(System.in, BS);
          }
      
          public FastScanner(String s) {
              try {
                  in = new BufferedInputStream(new FileInputStream(new File(s)), BS);
              } catch (Exception e) {
                  in = new BufferedInputStream(System.in, BS);
              }
          }
      
          char getChar() {
              while (bId == size) {
                  try {
                      size = in.read(buf);
                  } catch (Exception e) {
                      return NC;
                  }
                  if (size == -1) return NC;
                  bId = 0;
              }
              return (char) buf[bId++];
          }
      
          int nextInt() {
              return (int) nextLong();
          }
      
          long nextLong() {
              cnt = 1;
              boolean neg = false;
              if (c == NC) c = getChar();
              for (; (c < '0' || c > '9'); c = getChar()) {
                  if (c == '-') neg = true;
              }
              long res = 0;
              for (; c >= '0' && c <= '9'; c = getChar()) {
                  res = (res << 3) + (res << 1) + c - '0';
                  cnt *= 10;
              }
              return neg ? -res : res;
          }
      
          double nextDouble() {
              boolean neg = false;
              if (c == NC) c = getChar();
              for (; (c < '0' || c > '9'); c = getChar()) {
                  if (c == '-') neg = true;
              }
              double cur = nextLong();
              if (c != '.') {
                  return neg ? -cur : cur;
              } else {
                  double frac = nextLong() / cnt;
                  return neg ? -cur - frac : cur + frac;
              }
          }
      
          String next() {
              StringBuilder res = new StringBuilder();
              while (c <= 32) c = getChar();
              while (c > 32) {
                  res.append(c);
                  c = getChar();
              }
              return res.toString();
          }
      
          String nextLine() {
              StringBuilder res = new StringBuilder();
              while (c <= 32) c = getChar();
              while (c != '\n') {
                  res.append(c);
                  c = getChar();
              }
              return res.toString();
          }
      
          boolean hasNext() {
              if (c > 32) return true;
              while (true) {
                  c = getChar();
                  if (c == NC) return false;
                  else if (c > 32) return true;
              }
          }
      }
      
      static void ASSERT(boolean assertion, String message) {
          if (!assertion) throw new AssertionError(message);
      }
      
      static void ASSERT(boolean assertion) {
          if (!assertion) throw new AssertionError();
      }
  }