feat: Solution for Problem #450 - Delete Node in a BST

Author: milanpanchal

Swift/Problems/450_DeleteNodeInABST.playground/Contents.swift

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+/*:
+# 450. Delete Node in a BST [Medium]
+  https://leetcode.com/problems/delete-node-in-a-bst/
+
+ ---
+
+### Problem Statement:
+
+ 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.
+
+### 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
+ 
+ ```
+ 
+ ### Notes:
+ + Time complexity should be O(height of tree).
+
+ */
+
+
+import UIKit
+
+// Definition for a binary tree node.
+ public class TreeNode {
+     public var val: Int
+     public var left: TreeNode?
+     public var right: TreeNode?
+     public init() { self.val = 0; self.left = nil; self.right = nil; }
+     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
+     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+         self.val = val
+         self.left = left
+         self.right = right
+     }
+ }
+
+// 85 / 85 test cases passed.
+// Status: Accepted
+// Runtime: 80 ms
+// Memory Usage: 22.4 MB
+
+class Solution {
+    func deleteNode(_ root: TreeNode?, _ key: Int) -> TreeNode? {
+        
+        guard let root = root else {
+            return nil
+        }
+        
+        if root.val > key {
+            root.left = deleteNode(root.left, key)
+        } else if root.val < key {
+            root.right = deleteNode(root.right, key)
+        } else {
+            if root.left == nil {
+                return root.right
+            } else if root.right == nil {
+                return root.left
+            } else {
+                let minNode = findMin(root.right!)
+                root.val = minNode.val
+                root.right = deleteNode(root.right, root.val)
+            }
+        }
+        
+        return root
+    }
+    
+    func findMin(_ root: TreeNode) -> TreeNode {
+        var root = root
+        
+        while let leftNode = root.left {
+            root = leftNode
+        }
+        
+        return root
+    }
+}
+
+let node = TreeNode(5)
+node.left = TreeNode(3)
+node.right = TreeNode(6)
+node.left?.left = TreeNode(2)
+node.left?.right = TreeNode(4)
+node.right?.right = TreeNode(7)
+
+
+let sol = Solution()
+sol.deleteNode(node, 3)

Swift/Problems/450_DeleteNodeInABST.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>