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47 lines
1.2 KiB
Ruby
47 lines
1.2 KiB
Ruby
=begin
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File: binary_search_edge.rb
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Created Time: 2024-04-09
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Author: Blue Bean (lonnnnnnner@gmail.com)
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=end
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require_relative './binary_search_insertion'
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### 二分搜尋最左一個 target ###
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def binary_search_left_edge(nums, target)
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# 等價於查詢 target 的插入點
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i = binary_search_insertion(nums, target)
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# 未找到 target ，返回 -1
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return -1 if i == nums.length || nums[i] != target
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i # 找到 target ，返回索引 i
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end
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### 二分搜尋最右一個 target ###
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def binary_search_right_edge(nums, target)
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# 轉化為查詢最左一個 target + 1
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i = binary_search_insertion(nums, 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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j = i - 1
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# 未找到 target ，返回 -1
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return -1 if j == -1 || nums[j] != target
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j # 找到 target ，返回索引 j
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end
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### Driver Code ###
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if __FILE__ == $0
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# 包含重複元素的陣列
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nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15]
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puts "\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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index = binary_search_left_edge(nums, target)
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puts "最左一個元素 #{target} 的索引為 #{index}"
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index = binary_search_right_edge(nums, target)
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puts "最右一個元素 #{target} 的索引為 #{index}"
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end
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end
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