Practice Questions for Recursion | Set 1

Explain the functionality of following functions.

Question 1

int fun1(int x, int y)  
{ 
  if(x == 0) 
    return y; 
  else
    return fun1(x - 1,  x + y); 
} 

Answer: The function fun() calculates and returns ((1 + 2 … + x-1 + x) +y) which is x(x+1)/2 + y. For example if x is 5 and y is 2, then fun should return 15 + 2 = 17.

Question 2

//minimum index finder 
int minIndex(int arr[], int s, int e) 
{ 
    int sml = INT32_MAX; 
    int mindex; 
    for (int i = s; i < e; i++) 
    { 
        if (sml > arr[i]) 
        { 
            sml = arr[i]; 
            mindex = i; 
        } 
    } 
    return mindex; 
} 
  
void fun2(int arr[], int start_index, int end_index) 
{ 
  if(start_index >= end_index)    
     return; 
  int min_index;  
  int temp;  
  
  /*minIndex() returns index of minimum value in  
    array arr[start_index...end_index] */
  min_index = minIndex(arr, start_index, end_index); 
  
  temp = arr[start_index]; 
  arr[start_index] = arr[min_index]; 
  arr[min_index] = temp;         
  
  fun2(arr, start_index + 1, end_index); 
}      

Answer: The function fun2() is a recursive implementation of Selection Sort.

Please write comments if you find any of the answers/codes incorrect, or you want to share more information about the topics discussed above.

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