题解 | #删除一个二叉搜索树中的节点#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param key int整型 
     * @return TreeNode类
     */
    public TreeNode deleteNode (TreeNode root, int key) {
        // write code here
        if (null == root) {
            return root;
        }
        HashMap<TreeNode, TreeNode> fathersMap = new HashMap<>();
        fathersMap.put(root, root);
        TreeNode node = search(root, key, fathersMap);
        if (null == node) {
            return root;
        }
        else {
            if (node == root) {
                TreeNode tmpNode = null;
                if (null == node.left && null == node.right) {
                    tmpNode = null;
                }
                else if (null == node.left && null != node.right) {
                    tmpNode = node.right;
                }
                else if (null != node.left && null == node.right) {
                    tmpNode = node.left;
                }
                else {
                    tmpNode = node.right;
                    TreeNode help = tmpNode;
                    while (null != help.left) {
                        help = help.left;
                    }
                    help.left = node.left;
                }
                return tmpNode;
            }
            else {
                TreeNode fatherNode = fathersMap.get(node);
                TreeNode tmpNode = null;
                if (null == node.left && null == node.right) {
                    tmpNode = null;
                }
                else if (null == node.left && null != node.right) {
                    tmpNode = node.right;
                }
                else if (null != node.left && null == node.right) {
                    tmpNode = node.left;
                }
                else {
                    tmpNode = node.right;
                    TreeNode help = tmpNode;
                    while (null != help.left) {
                        help = help.left;
                    }
                    help.left = node.left;
                }
                if (fatherNode.left == node) {
                    fatherNode.left = tmpNode;
                }
                else {
                    fatherNode.right = tmpNode;
                }
                return root;
            }
        }
    }
    
    public TreeNode search(TreeNode node, int key, HashMap<TreeNode, TreeNode> fathersMap) {
        if (null == node) {
            return null;
        }
        else {
            if (node.val == key) {
                return node;
            }
            else if (node.val < key) {
                if (null != node.right) {
                    fathersMap.put(node.right, node);
                }
                return search(node.right, key, fathersMap);
            }
            else {
                if (null != node.left) {
                    fathersMap.put(node.left, node);
                }
                return search(node.left, key, fathersMap);
            }
        }
    }
}