Question

Java class TreeNode is defined as below:

public class TreeNode {
    public int val;
    public TreeNode left, right;
    public TreeNode(int x) { val = x; }
    public TreeNode(int x, TreeNode lChild, TreeNode rChild) {
        val = x;
        left = lChild;
        right = rChild;
    }
}

Suppose you only have the reference of the root, please write a method that returns a deep copy of the binary tree. Your method returns the root of the deep copy. Your algorithm should have time complexity of O( n ).

The code should be in java.

Answer 1

public class TreeNode {
    public int val;
    public TreeNode left, right;

    public TreeNode(int x) {
        val = x;
    }

    public TreeNode(int x, TreeNode lChild, TreeNode rChild) {
        val = x;
        left = lChild;
        right = rChild;
    }

    public TreeNode copy() {
        TreeNode leftCopy = null, rightCopy = null;
        if (left != null)
            leftCopy = left.copy();
        if (right != null)
            rightCopy = right.copy();
        return new TreeNode(val, leftCopy, rightCopy);
    }

    public static TreeNode copyTree(TreeNode root) {
        if (root == null)
            return null;
        else
            return root.copy();
    }
}