Leetcode 450 Delete Node in a BST
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2022-05-18 19:39:15
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Problem:
Given a root node reference of a BST and a key, delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST.
Basically, the deletion can be divided into two stages:
Search for a node to remove.
If the node is found, delete the node.
Note: Time complexity should be O(height of tree).
Ideas:
two steps for this problem:
- find the node
- If find, discuss how to delete:
- no child: return null
- one child: return child
- two child return the successor
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution1 {
public TreeNode deleteNode(TreeNode root, int key) {
if (root == null) return null;
if (root.val < key) {
// check the right node
root.right = deleteNode(root.right, key);
}else if (root.val > key) {
// check the left node
root.left = deleteNode(root.left, key);
}else {
// left node and right node are null
if (root.left == null && root.right == null) return null;
// left node is null
if (root.left == null) return root.right;
// right node is null
if (root.right == null) return root.left;
// left and right node are both not null
TreeNode minNode = findMin(root.right);
root.val = minNode.val;
root.right = deleteNode(root.right, root.val);
}
return root;
}
public TreeNode findMin(TreeNode root) {
while(root.left != null) {
root = root.left;
}
return root;
}
}