Pattern: BST

Delete a node in bst

/**
 * Definition for a binary tree node.
 * 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;
 *     }
 * }
 */
class Solution {
    public TreeNode deleteNode(TreeNode root, int key) {
        return update(root, null, key);
    }

    public TreeNode update(TreeNode root, TreeNode parent, int key){
        if(root==null) return root;
        if(root.val == key){
            TreeNode left = root.left;
            root  = root.right;
            return add(left,root);
        }
        root.left = update(root.left, root,key);
        root.right = update(root.right, root, key);
        return root;
    }

    public TreeNode add(TreeNode node, TreeNode root){
        if(node==null) return root;
        if(root ==null) return node;
        if(root.val > node.val){
            root.left = add(node, root.left);
        }
        else if(root.val < node.val){
            root.right = add(node, root.right);
        }
        return root;
    }
}