Lowest Common Ancestor of a Binary Tree Part

bottom-up

 

 

package test.ui;

import java.util.HashSet;
import java.util.Set;

public class test {
    //unsigned 2^32-1 so we need a long to instead.
      public class TreeNode {
              int val;
              TreeNode left;
              TreeNode right;
              TreeNode(int x) { val = x; }
      }
      public TreeNode LAC(TreeNode root, TreeNode l, TreeNode r){
          if(root == null)
              return null;
          if(root == l || root == r)
              return root;
          TreeNode left = LAC(root.left,l,r);
          TreeNode right = LAC(root.right,l,r);
          if(left!=null && right!=null)
              return root;
          return left!=null?left:right;
      }
      
      public TreeNode buildTree(){
          TreeNode root = new TreeNode(3);
          root.left = new TreeNode(5);
          root.right = new TreeNode(1);
          root.left.left = new TreeNode(6);
          root.left.right = new TreeNode(2);
          root.left.right.left = new TreeNode(7);
          root.left.right.right = new TreeNode(4);
          root.right.left = new TreeNode(0);
          root.right.right = new TreeNode(8);
          return root;
      }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        test t = new test();
        TreeNode root = t.buildTree();
        System.out.print(t.LAC(root, root.left.left, root.left.right.right).val);
    }

}