recursion problems (#361)

* pairs of integers whose sum is equal to number.  

find all pairs of integers whose sum is equal to a given number.

* permutation 

if two strings are in permutation , they have the same characters but in different order.

* add two sorted linked list 

add two sorted linked list and the new linked list too will be sorted.

* recursion problems

recursion problems

Author: divyaa1511

Python/5 recusrion problems.py

@@ -0,0 +1,71 @@
+# 1..TO FIND FACTORIAL OF A NUMBER USING RECURSION
+
+def factorial(n):
+    assert n>=0 and int(n)==n , "the number must be positive integer only"
+    if n==0 or n==1:
+        return 1
+    else:
+        return n*factorial(n-1)
+
+print(factorial(4))
+
+
+
+
+
+# 2..TO PRINT FIBONACCI SERIES
+
+def fibonacci(n):
+    assert n>=0 and int(n)==n , "only positive integers"
+    if n==0 or n==1:
+        return n
+    else:
+        return fibonacci(n-1) + fibonacci(n-2)
+
+print(fibonacci(8))
+
+
+
+
+
+# 3.. TO FIND IF THE GIVEN STRING IS PALINDROME OR NOT
+
+def isPalindrome(strng):
+    if len(strng)==0:
+        return True
+    if strng[0]==strng[-1]:
+        return isPalindrome(strng[1:-1])
+    
+    else:
+         return False
+print((isPalindrome('naman')))
+
+
+
+
+# 4..TO FIND THE SUM OF ALL DIGITS IN THE GIVEN NUMBER
+
+def sum(n):
+    assert n>=0 and int(n)==n , "only positive integers"
+    if n==0:
+        return 0
+    else:
+        return int(n%10) + sum(int(n//10))
+
+print(sum(11))
+
+
+
+
+# 5..TO FIND THE POWER OF A NUMBER
+
+def power(base,exp):
+    assert exp>=0 and int(exp)==exp , "power can only be positive integers"
+    if(exp==0):
+        return 1
+    if(exp==1):
+        return base
+    else:
+        return base*power(base,exp-1)
+
+print(power(2,5))