Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

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

        _______3______
       /              \
    ___5__          ___1__
   /      \        /      \
   6      _2       0       8
         /  \
         7   4

For example, the lowest common ancestor (LCA) of nodes5and1is3. Another example is LCA of nodes5and4is5, since a node can be a descendant of itself according to the LCA definition.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null) return null;

        TreeNode leftResult = lowestCommonAncestor(root.left, p, q);
        TreeNode rightResult = lowestCommonAncestor(root.right, p, q);

        if (root == p || root == q){
            return root;
        }
        else if (leftResult != null && rightResult != null){
            return root;
        }
        else if (leftResult != null){
            return leftResult;
        }
        else{
            return rightResult;
        }
    }
}