feat: Solution for August Challenge 24 - Sum of Left Leaves

Author: milanpanchal

Swift/August Challenge/24_SumOfLeftLeaves.playground/Contents.swift

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+/*:
+# Sum of Left Leaves
+  https://leetcode.com/explore/challenge/card/august-leetcoding-challenge/552/week-4-august-22nd-august-28th/3435/
+
+ ---
+
+### Problem Statement:
+
+ Find the sum of all left leaves in a given binary tree.
+
+### Example:
+
+ ```
+     3
+    / \
+   9  20
+     /  \
+    15   7
+
+ There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.
+
+ ```
+ */
+
+
+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
+    }
+}
+
+
+class Solution {
+    private var sum = 0
+    func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
+        guard let node = root else {
+            return 0
+        }
+        dfs(node, false)
+        return sum
+    }
+    
+    private func dfs(_ node: TreeNode?, _ isLeft: Bool) {
+        guard let node = node else { return }
+        
+        dfs(node.left, true)
+        
+        if node.left == nil, node.right == nil, isLeft {
+            sum += node.val
+        }
+        dfs(node.right, false)
+    }
+}
+
+class Solution2 {
+    
+    func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
+        return dfs(root, false)
+    }
+    
+    private func dfs(_ node: TreeNode?, _ isLeft: Bool) -> Int {
+        guard let node = node else { return 0 }
+        
+        if node.left == nil, node.right == nil, isLeft {
+            return node.val
+        }
+
+        return dfs(node.left, true) + dfs(node.right, false)
+    }
+}
+
+let node = TreeNode(3)
+node.left = TreeNode(9)
+node.right = TreeNode(20)
+node.right?.left = TreeNode(15)
+node.right?.right = TreeNode(7)
+
+let sol = Solution2()
+sol.sumOfLeftLeaves(node) // 24

Swift/August Challenge/24_SumOfLeftLeaves.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>