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/**
 * 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* solve(TreeNode* root, TreeNode* p, TreeNode* q){
        if(root==NULL) return NULL;
        if(root==p) return p;
        if(root==q) return q;

        TreeNode* left =solve(root->left,p,q);
        TreeNode* right=solve(root->right,p,q);

        if(left!=NULL && right!=NULL) return root;
        else if(left!=NULL) return left;
        else if(right!=NULL) return right;
        else return NULL;

    }

    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) { 
        return solve(root,p,q);
    }
};