Adds 783. Minimum Distance Between BST Nodes

Author: ivanlesko

783. Minimum Distance Between BST Nodes .playground/Contents.swift

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+import UIKit
+import UIKit
+
+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
+    }
+}
+
+/**
+ # Intuition
+ Use inorder DFS since the answer will always the minimum difference between two adjacent nodes in ascending order.
+
+ # Approach
+ Traverse the tree using DFS inorder traversal.
+ Store the previous visited node.
+ Find the difference between the current node and the previous node.
+
+ # Complexity
+ - Time complexity:
+ O(n) where `n` is `root.nodes.size`
+
+ - Space complexity:
+ O(1) or O(h) where `h` is the height of the tree
+ */
+
+class Solution {
+    
+    var prev: TreeNode?
+    
+    func evaluate(_ root: TreeNode?, _ currMin: inout Int) {
+        guard let root = root else {
+            return
+        }
+        
+        evaluate(root.left, &currMin)
+        if let prev = prev {
+            print(root.val, prev.val, root.val - prev.val)
+            currMin = min(currMin, root.val - prev.val)
+        }
+        prev = root
+        evaluate(root.right, &currMin)
+    }
+    
+    func minDiffInBST(_ root: TreeNode?) -> Int {
+        var ans = Int.max
+        evaluate(root, &ans)
+        return ans
+    }
+}

783. Minimum Distance Between BST Nodes .playground/contents.xcplayground

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