From 2ec4867125e60381b9ded470a59ad89d0b8401d1 Mon Sep 17 00:00:00 2001
From: YDLIN <1924723909@qq.com>
Date: Sat, 22 Jan 2022 10:26:18 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20404.=20=E5=B7=A6=E5=8F=B6?=
 =?UTF-8?q?=E5=AD=90=E4=B9=8B=E5=92=8C=20Swift=20=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0404.左叶子之和.md | 48 ++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/problems/0404.左叶子之和.md b/problems/0404.左叶子之和.md
index ddbd100e..09272052 100644
--- a/problems/0404.左叶子之和.md
+++ b/problems/0404.左叶子之和.md
@@ -373,6 +373,54 @@ var sumOfLeftLeaves = function(root) {
 ```
 
 
+## Swift 
+
+**递归法** 
+```swift
+func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+
+    let leftValue = sumOfLeftLeaves(root.left)
+    let rightValue = sumOfLeftLeaves(root.right)
+
+    var midValue: Int = 0
+    if root.left != nil && root.left?.left == nil && root.left?.right == nil {
+        midValue = root.left!.val
+    }
+
+    let sum = midValue + leftValue + rightValue
+    return sum
+}
+```
+**迭代法**
+```swift
+func sumOfLeftLeaves(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+
+    var stack = Array<TreeNode>()
+    stack.append(root)
+    var sum = 0
+
+    while !stack.isEmpty {
+        let lastNode = stack.removeLast()
+
+        if lastNode.left != nil && lastNode.left?.left == nil && lastNode.left?.right == nil {
+            sum += lastNode.left!.val
+        }
+        if let right = lastNode.right {
+            stack.append(right)
+        }
+        if let left = lastNode.left {
+            stack.append(left)
+        }
+    }
+    return sum
+}
+```