Lowest_Common_Ancestor.cpp

// A recursive CPP program to find 
// LCA of two nodes n1 and n2. 
#include <bits/stdc++.h> 
using namespace std; 

class node 
{ 
	public: 
	int data; 
	node* left, *right; 
}; 

/* Function to find LCA of n1 and n2. 
The function assumes that both 
n1 and n2 are present in BST */
node *lca(node* root, int n1, int n2) 
{ 
	if (root == NULL) return NULL; 

	// If both n1 and n2 are smaller 
	// than root, then LCA lies in left 
	if (root->data > n1 && root->data > n2) 
		return lca(root->left, n1, n2); 

	// If both n1 and n2 are greater than 
	// root, then LCA lies in right 
	if (root->data < n1 && root->data < n2) 
		return lca(root->right, n1, n2); 

	return root; 
} 

/* Helper function that allocates 
a new node with the given data.*/
node* newNode(int data) 
{ 
	node* Node = new node(); 
	Node->data = data; 
	Node->left = Node->right = NULL; 
	return(Node); 
} 

/* Driver code*/
int main() 
{ 
	// Let us construct the BST 
	// shown in the above figure 
	node *root = newNode(20); 
	root->left = newNode(8); 
	root->right = newNode(22); 
	root->left->left = newNode(4); 
	root->left->right = newNode(12); 
	root->left->right->left = newNode(10); 
	root->left->right->right = newNode(14); 

	int n1 = 10, n2 = 14; 
	node *t = lca(root, n1, n2); 
	cout << "LCA of " << n1 << " and " << n2 << " is " << t->data<<endl; 

	n1 = 14, n2 = 8; 
	t = lca(root, n1, n2); 
	cout<<"LCA of " << n1 << " and " << n2 << " is " << t->data << endl; 

	n1 = 10, n2 = 22; 
	t = lca(root, n1, n2); 
	cout << "LCA of " << n1 << " and " << n2 << " is " << t->data << endl; 
	return 0; 
}