Add figures to replace_linear_by_hashing.md

codes/swift/chapter_searching/two_sum.swift

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+/**
+ * File: two_sum.swift
+ * Created Time: 2023-01-03
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 方法一：暴力枚举 */
+func twoSumBruteForce(nums: [Int], target: Int) -> [Int] {
+    // 两层循环，时间复杂度 O(n^2)
+    for i in nums.indices.dropLast() {
+        for j in nums.indices.dropFirst(i + 1) {
+            if nums[i] + nums[j] == target {
+                return [i, j]
+            }
+        }
+    }
+    return [0]
+}
+
+/* 方法二：辅助哈希表 */
+func twoSumHashTable(nums: [Int], target: Int) -> [Int] {
+    // 辅助哈希表，空间复杂度 O(n)
+    var dic: [Int: Int] = [:]
+    // 单层循环，时间复杂度 O(n)
+    for i in nums.indices {
+        if let j = dic[target - nums[i]] {
+            return [j, i]
+        }
+        dic[nums[i]] = i
+    }
+    return [0]
+}
+
+@main
+enum LeetcodeTwoSum {
+    /* Driver Code */
+    static func main() {
+        // ======= Test Case =======
+        let nums = [2, 7, 11, 15]
+        let target = 13
+        // ====== Driver Code ======
+        // 方法一
+        var res = twoSumBruteForce(nums: nums, target: target)
+        print("方法一 res = \(res)")
+        // 方法二
+        res = twoSumHashTable(nums: nums, target: target)
+        print("方法二 res = \(res)")
+    }
+}