Feature/chapter divide and conquer swift (#719)

* feat: add Swift codes for binary_search_recur article

* feat: add Swift codes for build_binary_tree_problem article

* feat: add Swift codes for hanota_problem article

codes/swift/chapter_divide_and_conquer/binary_search_recur.swift

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+/**
+ * File: binary_search_recur.swift
+ * Created Time: 2023-09-02
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 二分查找：问题 f(i, j) */
+func dfs(nums: [Int], target: Int, i: Int, j: Int) -> Int {
+    // 若区间为空，代表无目标元素，则返回 -1
+    if i > j {
+        return -1
+    }
+    // 计算中点索引 m
+    let m = (i + j) / 2
+    if nums[m] < target {
+        // 递归子问题 f(m+1, j)
+        return dfs(nums: nums, target: target, i: m + 1, j: j)
+    } else if nums[m] > target {
+        // 递归子问题 f(i, m-1)
+        return dfs(nums: nums, target: target, i: i, j: m - 1)
+    } else {
+        // 找到目标元素，返回其索引
+        return m
+    }
+}
+
+/* 二分查找 */
+func binarySearch(nums: [Int], target: Int) -> Int {
+    let n = nums.count
+    // 求解问题 f(0, n-1)
+    return dfs(nums: nums, target: target, i: 0, j: n - 1)
+}
+
+@main
+enum BinarySearchRecur {
+    /* Driver Code */
+    static func main() {
+        let target = 6
+        let nums = [1, 3, 6, 8, 12, 15, 23, 26, 31, 35]
+
+        // 二分查找（双闭区间）
+        let index = binarySearch(nums: nums, target: target)
+        print("目标元素 6 的索引 = \(index)")
+    }
+}