LCA in binary tree

Author: TonyStark-19

Tree/LCAInBinaryTree.cpp

@@ -0,0 +1,98 @@
+#include <iostream>
+#include <vector>
+using namespace std;
+
+// Node class
+class Node
+{
+public:
+    int data;
+    Node *left;
+    Node *right;
+
+    Node(int val)
+    {
+        data = val;
+        left = right = NULL;
+    }
+};
+
+static int idx = -1;
+
+// Build tree from preorder traversal
+Node *buildTree(vector<int> preorder)
+{
+    idx++;
+
+    // base case
+    if (preorder[idx] == -1)
+    {
+        return NULL;
+    }
+
+    // create root node
+    Node *root = new Node(preorder[idx]);
+
+    // left subtree
+    root->left = buildTree(preorder);
+
+    // right subtree
+    root->right = buildTree(preorder);
+
+    return root;
+}
+
+// Find a node with a given value
+Node *findNode(Node *root, int val)
+{
+    if (root == NULL)
+        return NULL;
+
+    if (root->data == val)
+        return root;
+
+    Node *leftResult = findNode(root->left, val);
+    if (leftResult != NULL)
+        return leftResult;
+
+    return findNode(root->right, val);
+}
+
+// Lowest common ancestor function
+Node *lowestCommonAncestor(Node *root, Node *p, Node *q)
+{
+    if (root == NULL)
+        return NULL;
+
+    if (root->data == p->data || root->data == q->data)
+        return root;
+
+    Node *leftLCA = lowestCommonAncestor(root->left, p, q);
+    Node *rightLCA = lowestCommonAncestor(root->right, p, q);
+
+    if (leftLCA && rightLCA)
+        return root;
+    else if (leftLCA != NULL)
+        return leftLCA;
+    else
+        return rightLCA;
+}
+
+int main()
+{
+    vector<int> preorder = {1, 2, 7, -1, -1, -1, 3, 4, -1, -1, 5, -1, -1};
+    Node *root = buildTree(preorder);
+
+    // Find two nodes
+    Node *p = findNode(root, 4);
+    Node *q = findNode(root, 5);
+
+    // Find and print LCA
+    Node *lca = lowestCommonAncestor(root, p, q);
+    if (lca != NULL)
+        cout << "Lowest Common Ancestor: " << lca->data << endl;
+    else
+        cout << "Lowest Common Ancestor not found." << endl;
+
+    return 0;
+}