52 lines
1.5 KiB
Swift
52 lines
1.5 KiB
Swift
/**
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* File: binary_search_edge.swift
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* Created Time: 2023-08-06
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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import binary_search_insertion_target
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/* 二分搜尋最左一個 target */
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func binarySearchLeftEdge(nums: [Int], target: Int) -> Int {
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// 等價於查詢 target 的插入點
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let i = binarySearchInsertion(nums: nums, target: target)
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// 未找到 target ，返回 -1
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if i == nums.endIndex || nums[i] != target {
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return -1
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}
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// 找到 target ，返回索引 i
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return i
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}
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/* 二分搜尋最右一個 target */
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func binarySearchRightEdge(nums: [Int], target: Int) -> Int {
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// 轉化為查詢最左一個 target + 1
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let i = binarySearchInsertion(nums: nums, target: target + 1)
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// j 指向最右一個 target ，i 指向首個大於 target 的元素
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let j = i - 1
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// 未找到 target ，返回 -1
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if j == -1 || nums[j] != target {
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return -1
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}
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// 找到 target ，返回索引 j
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return j
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}
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@main
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enum BinarySearchEdge {
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/* Driver Code */
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static func main() {
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// 包含重複元素的陣列
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let nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15]
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print("\n陣列 nums = \(nums)")
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// 二分搜尋左邊界和右邊界
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for target in [6, 7] {
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var index = binarySearchLeftEdge(nums: nums, target: target)
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print("最左一個元素 \(target) 的索引為 \(index)")
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index = binarySearchRightEdge(nums: nums, target: target)
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print("最右一個元素 \(target) 的索引為 \(index)")
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}
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}
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}
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