0450-delete-node-in-a-bst.ts

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function deleteNode(root: TreeNode | null, key: number): TreeNode | null {
    if (!root) {
        return root;
    }

    if (key > root.val) {
        root.right = deleteNode(root.right, key);
    } else if (key < root.val) {
        root.left = deleteNode(root.left, key);
    } else {
        if (!root.right) {
            return root.left;
        } else if (!root.left) {
            return root.right;
        } else {
            let minNode = minValueNode(root.right);
            root.val = minNode.val;
            root.right = deleteNode(root.right, minNode.val);
        }
    }
    return root;
}

function minValueNode(root: TreeNode): TreeNode {
    let curr: TreeNode = root;
    while (curr && curr.left) {
        curr = curr.left;
    }
    return curr;
}