Lowest Common Ancestor

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 func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
     if root == nil || root == p || root == q {
         return root 
     }
     left := lowestCommonAncestor(root.Left,p,q)
     right := lowestCommonAncestor(root.Right,p,q)
     if left != nil && right != nil {
         return root 
     }
     if left != nil{
         return left 
     } else{
         return right 
     }
}