diff --git a/codes/swift/Package.swift b/codes/swift/Package.swift index 0ff7baec..1190e534 100644 --- a/codes/swift/Package.swift +++ b/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"]), diff --git a/codes/swift/chapter_searching/binary_search_edge.swift b/codes/swift/chapter_searching/binary_search_edge.swift new file mode 100644 index 00000000..504f84f4 --- /dev/null +++ b/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)") + } +}