feat: add Swift codes for binary_search_edge article (#518)

codes/swift/Package.swift

@@ -42,6 +42,7 @@ let package = Package(
         .executable(name: "graph_dfs", targets: ["graph_dfs"]),
         // chapter_searching
         .executable(name: "binary_search", targets: ["binary_search"]),
+        .executable(name: "binary_search_edge", targets: ["binary_search_edge"]),
         .executable(name: "two_sum", targets: ["two_sum"]),
         .executable(name: "linear_search", targets: ["linear_search"]),
         .executable(name: "hashing_search", targets: ["hashing_search"]),
@@ -103,6 +104,7 @@ let package = Package(
         .executableTarget(name: "graph_dfs", dependencies: ["utils", "graph_adjacency_list_target"], path: "chapter_graph", sources: ["graph_dfs.swift"]),
         // chapter_searching
         .executableTarget(name: "binary_search", path: "chapter_searching", sources: ["binary_search.swift"]),
+        .executableTarget(name: "binary_search_edge", path: "chapter_searching", sources: ["binary_search_edge.swift"]),
         .executableTarget(name: "two_sum", path: "chapter_searching", sources: ["two_sum.swift"]),
         .executableTarget(name: "linear_search", dependencies: ["utils"], path: "chapter_searching", sources: ["linear_search.swift"]),
         .executableTarget(name: "hashing_search", dependencies: ["utils"], path: "chapter_searching", sources: ["hashing_search.swift"]),

codes/swift/chapter_searching/binary_search_edge.swift

@@ -0,0 +1,64 @@
+/**
+ * File: binary_search_edge.swift
+ * Created Time: 2023-05-28
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 二分查找最左一个元素 */
+func binarySearchLeftEdge(nums: [Int], target: Int) -> Int {
+    // 初始化双闭区间 [0, n-1]
+    var i = 0
+    var j = nums.count - 1
+    while i <= j {
+        let m = i + (j - 1) / 2 // 计算中点索引 m
+        if nums[m] < target {
+            i = m + 1 // target 在区间 [m+1, j] 中
+        } else if nums[m] > target {
+            j = m - 1 // target 在区间 [i, m-1] 中
+        } else {
+            j = m - 1 // 首个小于 target 的元素在区间 [i, m-1] 中
+        }
+    }
+    if i == nums.count || nums[i] != target {
+        return -1 // 未找到目标元素，返回 -1
+    }
+    return i
+}
+
+/* 二分查找最右一个元素 */
+func binarySearchRightEdge(nums: [Int], target: Int) -> Int {
+    // 初始化双闭区间 [0, n-1]
+    var i = 0
+    var j = nums.count - 1
+    while i <= j {
+        let m = i + (j - i) / 2 // 计算中点索引 m
+        if nums[m] < target {
+            i = m + 1 // target 在区间 [m+1, j] 中
+        } else if nums[m] > target {
+            j = m - 1 // target 在区间 [i, m-1] 中
+        } else {
+            i = m + 1 // 首个大于 target 的元素在区间 [m+1, j] 中
+        }
+    }
+    if j < 0 || nums[j] != target {
+        return -1 // 未找到目标元素，返回 -1
+    }
+    return j
+}
+
+@main
+enum BinarySearchEdge {
+    /* Driver Code */
+    static func main() {
+        let target = 6
+        let nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15]
+
+        // 二分查找最左一个元素
+        let indexLeft = binarySearchLeftEdge(nums: nums, target: target)
+        print("数组中最左一个元素 6 的索引 = \(indexLeft)")
+
+        // 二分查找最右一个元素
+        let indexRight = binarySearchRightEdge(nums: nums, target: target)
+        print("数组中最右一个元素 6 的索引 = \(indexRight)")
+    }
+}