Top//Answer-14A-1

Answer to Question 14A-1

When a and b are close to one another, the part to reverse is small. If a > b, the range is empty, and there is nothing to do. If a = b, there is just one thing, and again there is nothing to do.

If a < b, the values in A[a] and A[b] need to be swapped. Then reverse the values in between, A[a+1], … A[b−1]. Here is an illustration for a = 10 and b = 16. The first step is to swap the first and last values, and the second step is the entire recursive call with a = 11 and b = 15.

A
10  41 
11  32 
12  80 
13  64 
14  18 
15  24 
16  45 
→
A
10  45 
11  32 
12  80 
13  64 
14  18 
15  24 
16  41 
→
A
10  45 
11  24 
12  18 
13  64 
14  80 
15  32 
16  45 

Here is a definition of reverse using those ideas. 

  void reverse(int A[], const int a, const int b)
  {
     if(a < b)
     {
       int t = A[a];
       A[a] = A[b];
       A[b] = t;
       reverse(A, a+1, b-1);
     }
  }