mirror of
https://github.com/krahets/hello-algo.git
synced 2024-12-26 11:46:29 +08:00
3f4220de81
* preorder, inorder, postorder -> pre-order, in-order, post-order * Bug fixes * Bug fixes * Update what_is_dsa.md * Sync zh and zh-hant versions * Sync zh and zh-hant versions. * Update performance_evaluation.md and time_complexity.md * Add @khoaxuantu to the landing page. * Sync zh and zh-hant versions * Add @ khoaxuantu to the landing page of zh-hant and en versions.
51 lines
1.5 KiB
Ruby
51 lines
1.5 KiB
Ruby
=begin
|
|
File: subset_sum_ii.rb
|
|
Created Time: 2024-05-22
|
|
Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
|
|
=end
|
|
|
|
### 回溯演算法：子集和 II ###
|
|
def backtrack(state, target, choices, start, res)
|
|
# 子集和等於 target 時，記錄解
|
|
if target.zero?
|
|
res << state.dup
|
|
return
|
|
end
|
|
|
|
# 走訪所有選擇
|
|
# 剪枝二：從 start 開始走訪，避免生成重複子集
|
|
# 剪枝三：從 start 開始走訪，避免重複選擇同一元素
|
|
for i in start...choices.length
|
|
# 剪枝一：若子集和超過 target ，則直接結束迴圈
|
|
# 這是因為陣列已排序，後邊元素更大，子集和一定超過 target
|
|
break if target - choices[i] < 0
|
|
# 剪枝四：如果該元素與左邊元素相等，說明該搜尋分支重複，直接跳過
|
|
next if i > start && choices[i] == choices[i - 1]
|
|
# 嘗試：做出選擇，更新 target, start
|
|
state << choices[i]
|
|
# 進行下一輪選擇
|
|
backtrack(state, target - choices[i], choices, i + 1, res)
|
|
# 回退：撤銷選擇，恢復到之前的狀態
|
|
state.pop
|
|
end
|
|
end
|
|
|
|
### 求解子集和 II ###
|
|
def subset_sum_ii(nums, target)
|
|
state = [] # 狀態（子集）
|
|
nums.sort! # 對 nums 進行排序
|
|
start = 0 # 走訪起始點
|
|
res = [] # 結果串列（子集串列）
|
|
backtrack(state, target, nums, start, res)
|
|
res
|
|
end
|
|
|
|
### Driver Code ###
|
|
if __FILE__ == $0
|
|
nums = [4, 4, 5]
|
|
target = 9
|
|
res = subset_sum_ii(nums, target)
|
|
|
|
puts "輸入陣列 nums = #{nums}, target = #{target}"
|
|
puts "所有和等於 #{target} 的子集 res = #{res}"
|
|
end
|