feat: add swift implementation to lcci problem: No.04.04

lcci/04.04.Check Balance/README.md

@@ -167,6 +167,40 @@ function isBalanced(root: TreeNode | null): boolean {
 }
 ```
 
+```swift
+/* class TreeNode {
+*    var val: Int
+*    var left: TreeNode?
+*    var right: TreeNode?
+*
+*    init(_ val: Int) {
+*        self.val = val
+*        self.left = nil
+*        self.right = nil
+*    }
+*  }
+*/
+
+class Solution {
+    func isBalanced(_ root: TreeNode?) -> Bool {
+        return dfs(root) >= 0
+    }
+
+    private func dfs(_ root: TreeNode?) -> Int {
+        guard let root = root else {
+            return 0
+        }
+
+        let leftHeight = dfs(root.left)
+        let rightHeight = dfs(root.right)
+        if leftHeight < 0 || rightHeight < 0 || abs(leftHeight - rightHeight) > 1 {
+            return -1
+        }
+        return max(leftHeight, rightHeight) + 1
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/04.04.Check Balance/README_EN.md

@@ -210,6 +210,40 @@ function isBalanced(root: TreeNode | null): boolean {
 }
 ```
 
+```swift
+/* class TreeNode {
+*    var val: Int
+*    var left: TreeNode?
+*    var right: TreeNode?
+*
+*    init(_ val: Int) {
+*        self.val = val
+*        self.left = nil
+*        self.right = nil
+*    }
+*  }
+*/
+
+class Solution {
+    func isBalanced(_ root: TreeNode?) -> Bool {
+        return dfs(root) >= 0
+    }
+
+    private func dfs(_ root: TreeNode?) -> Int {
+        guard let root = root else {
+            return 0
+        }
+
+        let leftHeight = dfs(root.left)
+        let rightHeight = dfs(root.right)
+        if leftHeight < 0 || rightHeight < 0 || abs(leftHeight - rightHeight) > 1 {
+            return -1
+        }
+        return max(leftHeight, rightHeight) + 1
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/04.04.Check Balance/Solution.swift

@@ -0,0 +1,31 @@
+/* class TreeNode {
+*    var val: Int
+*    var left: TreeNode?
+*    var right: TreeNode?
+*    
+*    init(_ val: Int) {
+*        self.val = val
+*        self.left = nil
+*        self.right = nil
+*    }
+*  } 
+*/
+
+class Solution {
+    func isBalanced(_ root: TreeNode?) -> Bool {
+        return dfs(root) >= 0
+    }
+
+    private func dfs(_ root: TreeNode?) -> Int {
+        guard let root = root else {
+            return 0
+        }
+
+        let leftHeight = dfs(root.left)
+        let rightHeight = dfs(root.right)
+        if leftHeight < 0 || rightHeight < 0 || abs(leftHeight - rightHeight) > 1 {
+            return -1
+        }
+        return max(leftHeight, rightHeight) + 1
+    }
+}