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38 lines
876 B
38 lines
876 B
=begin
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File: climbing_stairs_backtrack.rb
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Created Time: 2024-05-29
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Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
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=end
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### 回溯 ###
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def backtrack(choices, state, n, res)
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# 當爬到第 n 階時，方案數量加 1
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res[0] += 1 if state == n
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# 走訪所有選擇
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for choice in choices
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# 剪枝：不允許越過第 n 階
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next if state + choice > n
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# 嘗試：做出選擇，更新狀態
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backtrack(choices, state + choice, n, res)
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end
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# 回退
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end
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### 爬樓梯：回溯 ###
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def climbing_stairs_backtrack(n)
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choices = [1, 2] # 可選擇向上爬 1 階或 2 階
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state = 0 # 從第 0 階開始爬
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res = [0] # 使用 res[0] 記錄方案數量
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backtrack(choices, state, n, res)
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res.first
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end
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### Driver Code ###
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if __FILE__ == $0
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n = 9
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res = climbing_stairs_backtrack(n)
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puts "爬 #{n} 階樓梯共有 #{res} 種方案"
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end
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