delete-node-in-a-bst.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} key
 * @return {TreeNode}
 */
var deleteNode = function (root, key) {
  if (!root) return null;
  if (key > root.val) {
    root.right = deleteNode(root.right, key);
    return root;
  } else if (key < root.val) {
    root.left = deleteNode(root.left, key);
    return root;
  } else {
    // 场景1: 该节点是叶节点
    if (!root.left && !root.right) {
      return null;
    }
    // 场景2: 有一个孩子节点不存在
    if (root.left && !root.right) {
      return root.left;
    } else if (root.right && !root.left) {
      return root.right;
    }
    // 场景3: 左右节点都存在
    const rightNode = root.right;
    // 获取最小值节点
    const minNode = getMinNode(rightNode);
    // 将待删除节点的值替换为最小值节点值
    root.val = minNode.val;
    // 删除最小值节点
    root.right = deleteNode(root.right, minNode.val);
    return root;
  }
};

function getMinNode(root) {
  while (root.left) {
    root = root.left;
  }
  return root;
}