Find Pairs with Given Sum in Different BSTs in Python

Suppose we have two given Binary Search Trees and another sum is given; we have to find pairs with respect of given sum so that each pair elements must be in different BSTs.

So, if the input is like sum = 12

then the output will be [(6, 6), (7, 5), (9, 3)]

To solve this, we will follow these steps −

• Define a function solve() . This will take trav1, trav2, Sum

• left := 0

• right := size of trav2 - 1

• res := a new list

• while left < size of trav1 and right >= 0, do

  • if trav1[left] + trav2[right] is same as Sum, then

    • insert (trav1[left],trav2[right]) at the end of res

    • left := left + 1

    • right := right - 1

  • otherwise when (trav1[left] + trav2[right]) < Sum, then

    • left := left + 1

  • otherwise,

    • right := right - 1

• return res

• From the main method do the following −

• trav1 := a new list, trav2 := a new list

• trav1 := in order traversal of tree1

• trav2 := in order traversal of tree2

• return solve(trav1, trav2, Sum)

Example (Python)

Let us see the following implementation to get better understanding −

 Live Demo

class ListNode:
   def __init__(self, data):
      self.data = data
      self.left = None
      self.right = None
def insert(root, key):
   if root == None:
      return ListNode(key)
   if root.data > key:
      root.left = insert(root.left, key)
   else:
      root.right = insert(root.right, key)
   return root
def storeInorder(ptr, traversal):
   if ptr == None:
      return
   storeInorder(ptr.left, traversal)
   traversal.append(ptr.data)
   storeInorder(ptr.right, traversal)
def solve(trav1, trav2, Sum):
   left = 0
   right = len(trav2) - 1
   res = []
   while left < len(trav1) and right >= 0:
      if trav1[left] + trav2[right] == Sum:
         res.append((trav1[left],trav2[right]))
         left += 1
         right -= 1
      elif trav1[left] + trav2[right] < Sum:
         left += 1
      else:
         right -= 1
   return res
def get_pair_sum(root1, root2, Sum):
   trav1 = []
   trav2 = []
   storeInorder(root1, trav1)
   storeInorder(root2, trav2)
   return solve(trav1, trav2, Sum)
root1 = None
   for element in [9,11,4,7,2,6,15,14]:
   root1 = insert(root1, element)
root2 = None
   for element in [6,19,3,2,4,5]:
   root2 = insert(root2, element)
Sum = 12
print(get_pair_sum(root1, root2, Sum))

Input

[9,11,4,7,2,6,15,14], [6,19,3,2,4,5], 12

Output

[(6, 6), (7, 5), (9, 3)]