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450. Delete Node in a BST
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).
Example:
root = [5,3,6,2,4,null,7] key = 3 5 / 3 6 / \ 2 4 7 Given key to delete is 3. So we find the node with value 3 and delete it. One valid answer is [5,4,6,2,null,null,7], shown in the following BST. 5 / 4 6 / 2 7 Another valid answer is [5,2,6,null,4,null,7]. 5 / 2 6 \ 4 7
Recursively find the node that has the same value as the key, while setting the left/right nodes equal to the returned subtree
Once the node is found, have to handle the below 4 cases
node doesn‘t have left or right - return null
node only has left subtree- return the left subtree
node only has right subtree- return the right subtree
node has both left and right - find the minimum value in the right subtree, set that value to the currently found node, then recursively delete the minimum value in the right subtree
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ /** * Recursively find the node that has the same value as the key, while setting the left/right nodes equal to the returned subtree Once the node is found, have to handle the below 4 cases node doesn‘t have left or right - return null node only has left subtree- return the left subtree node only has right subtree- return the right subtree node has both left and right - find the minimum value in the right subtree, set that value to the currently found node, then recursively delete the minimum value in the right subtree */ public class Solution { public TreeNode deleteNode(TreeNode root, int key) { if(root == null) return null; if(key < root.val){ root.left = deleteNode(root.left, key); } else if(key > root.val){ root.right = deleteNode(root.right, key); } else{ //equal if(root.left == null && root.right == null) return null; else if(root.left == null) return root.right; else if(root.right == null) return root.left; else{ TreeNode minRight = getMin(root.right); root.val = minRight.val; root.right = deleteNode(root.right, minRight.val); } } return root; } public TreeNode getMin(TreeNode root){ while(root.left != null){ root = root.left; } return root; } }
450. Delete Node in a BST