Added Basic Array Questions

recursion/Basic Array Questions/Display_arr_reverse.py

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+# Program to print an array in reverse order
+
+def reverse(a,n):
+    if n==0: # Base Case when size of array is 0 then it returns
+        return
+    else:
+        print(a[n-1],end=" ") # Print the last element of the array
+        reverse(a,n-1) # Function calling itself 
+
+a = [1, 42, 45, 60, 50, 10, 2] # Taking an array
+n = len(a)
+reverse(a,n)
+
+# Output
+# 2 10 50 60 45 42 1

recursion/Basic Array Questions/Display_array.py

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+# Program to Display Array Elements Using Recursion
+
+def display_arr(a,i,n):
+    if i>=n: # Base Case if value of i become greater or equal to size of an array then it returns
+        return
+    print(a[i],end=" ") # Print the array at ith position (as the value of i increases elements get print accordingly)
+    display_arr(a,i+1,n) # Function calling itself
+
+arr = [] # Taking an Array
+n = int(input("Enter the size of the array: ")) # Initializing the size of an array
+print("Enter the elements of the array: ")
+for i in range(0,n):
+    num = int(input()) # Taking input from user 
+    arr.append(num)
+
+print("Elements of Array are: ") 
+display_arr(arr,0,n) # Printing the elements of an array through recursion
+
+# Example
+
+# Input: 
+# 1
+# 2
+# 3
+# 4
+# 5
+
+# Ouput:
+# 1 2 3 4 5

recursion/Basic Array Questions/First_Index.py

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+# Program to find first index of occurrence of an element in an array
+# Using start index approach, in this we don't have to make the copy of an array
+
+
+def firstindex(a, x, si):
+    l = len(a)
+    if si==l: # Base Case if size of array is 1 then it returns -1
+        return -1
+    if a[si]==x: # If element at the index si is equal to the value of x 
+        return si # Then it will return index si
+    return firstindex(a,x,si+1) # Function calling itself with the increment of si
+
+a = [1,4,3,7,5,4,6] # Taking an Example
+x = 4 # Find the first index of occurrence of 4
+print(firstindex(a, x,0))
+
+# Ouput: 
+# 1

recursion/Basic Array Questions/Last_Index.py

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+# Program to find last index of occurrence of an element in an array
+# We will use start index approach
+
+def lastindex(a, x, si):
+    l = len(a)
+    if si==l: # Base Case if size of array is 1 then it returns -1
+        return -1
+
+    smallerListOutput = lastindex(a, x, si+1) # calling function itself
+
+    if smallerListOutput != -1: # if smallerListOuput returns -1 then it will return smallerListOuput itself
+        return smallerListOutput # means when in smallerListOuput, value of si becomes equal to length of array
+        # it means no element found then it will return -1
+    else:
+        if a[si]==x: # if element at si is equal to x then it will return index si
+            return si
+        else:
+            return -1 # else return -1
+
+a = [1,2,4,6,7,8,4,7,6] # Taking an array for example
+x = 4 # Find the last index of occurrence of 4
+print(lastindex(a,x,0))
+
+# Output:
+# 6

recursion/Basic Array Questions/Max_arr.py

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+# Program to find maximum element in an array using recursion
+
+def max_arr_rec(a,n):
+    if n==1: # Base Case if array containing only one element then return it
+        return a[0]
+    else:
+        previous = max_arr_rec(a,n-1) # calling function itself and storing in variable called prevoius
+        current = a[n-1] # that means previous element from the sequence and check the value with the next element in the sequence which is current
+        if previous > current: # comparing both and returing the max of these values
+            return previous
+        else: 
+            return current
+
+a = [1, 42, 45, 60, 50, 10, 2] # Taking an array for example
+n = len(a) # length of the array
+print(max_arr_rec(a,n))
+
+# Output:
+# 60