Lowest Common Ancestor of a Binary Tree.cpp

/* 
    Solution by Rahul Surana
    
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Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes
p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”



    ***********************************************************
*/


#include <bits/stdc++.h>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    
    
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
       if(root == NULL) return NULL;
        if(root->val == p->val || root-> val == q->val){
            return root;
        }
        TreeNode* n1 = lowestCommonAncestor(root->left,p,q);
        TreeNode* n2 = lowestCommonAncestor(root->right,p,q);
        if(n1&&n2) return root;
        if(n1) return n1;
        if(n2) return n2;
        return NULL;
    }
};