Merge pull request #186 from dsrao711/issue_185

Python solution for lowest common ancestor in DSA 450

Author: smv1999

DSA 450 GFG/lowest_common_ancestor.py

@@ -0,0 +1,94 @@
+# Link to the problem : https://practice.geeksforgeeks.org/problems/lowest-common-ancestor-in-a-bst/1
+
+
+
+#Function to find the lowest common ancestor in a BST. 
+def LCA(root, n1, n2):
+    #code here.
+    while(root):
+        if(root.data > n1 and root.data > n2):
+            root = root.left
+        elif(root.data < n1 and root.data < n2):
+            root = root.right
+        else:
+            break
+    return root
+
+#{ 
+#  Driver Code Starts
+#Initial Template for Python 3
+from collections import deque
+# Tree Node
+class Node:
+    def __init__(self, val):
+        self.right = None
+        self.data = val
+        self.left = None
+
+# Function to Build Tree   
+def buildTree(s):
+    #Corner Case
+    if(len(s)==0 or s[0]=="N"):           
+        return None
+        
+    # Creating list of strings from input 
+    # string after spliting by space
+    ip=list(map(str,s.split()))
+    
+    # Create the root of the tree
+    root=Node(int(ip[0]))                     
+    size=0
+    q=deque()
+    
+    # Push the root to the queue
+    q.append(root)                            
+    size=size+1 
+    
+    # Starting from the second element
+    i=1                                       
+    while(size>0 and i<len(ip)):
+        # Get and remove the front of the queue
+        currNode=q[0]
+        q.popleft()
+        size=size-1
+        
+        # Get the current node's value from the string
+        currVal=ip[i]
+        
+        # If the left child is not null
+        if(currVal!="N"):
+            
+            # Create the left child for the current node
+            currNode.left=Node(int(currVal))
+            
+            # Push it to the queue
+            q.append(currNode.left)
+            size=size+1
+        # For the right child
+        i=i+1
+        if(i>=len(ip)):
+            break
+        currVal=ip[i]
+        
+        # If the right child is not null
+        if(currVal!="N"):
+            
+            # Create the right child for the current node
+            currNode.right=Node(int(currVal))
+            
+            # Push it to the queue
+            q.append(currNode.right)
+            size=size+1
+        i=i+1
+    return root
+    
+    
+if __name__=="__main__":
+    t=int(input())
+    for _ in range(0,t):
+        s=input()
+        root=buildTree(s)
+        n1,n2=list(map(int,input().split()))
+        print(LCA(root,n1,n2).data);
+        
+# } Driver Code Ends