DeleteNodeInABst.java

package com.dbc.code;

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

        TreeNode() {
        }

        TreeNode(int val) {
            this.val = val;
        }

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

    public TreeNode deleteNode(TreeNode root, int key) {
        if (root == null) return null;
        else if (root.val < key) root.right = deleteNode(root.right, key);
        else if (root.val > key) root.left = deleteNode(root.left, key);
        else if (root.left == null || root.right == null) root = root.left != null ? root.left : root.right;
        else {
            TreeNode node = root.right;
            while (node.left != null) {
                node = node.left;
            }
            node.left = root.left;
            return root.right;
        }
        return root;
    }
}