Create LowestCommonAncestorBST.cpp

Trees and Graphs/LowestCommonAncestorBST.cpp

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+// 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;
+}
+
+// This code is contributed by Bhanu Pratap Singh