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coin change problem solver in ruby
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| # code modified from https://github.com/nelsonic/coin-change-ruby | |
| class Change | |
| def change(amount, available_coins = [100, 50, 25, 10, 5, 1]) | |
| @available_coins = available_coins | |
| smallest = @available_coins.min | |
| zeros = [0] * @available_coins.size | |
| solutions = (0...@available_coins.size).map { |n| k = zeros.dup; k[n] = 1; k } | |
| vectors = solutions.dup | |
| visited = Hash[solutions.map { |v| [v, true] }] | |
| scores = Hash[@available_coins.map { |n| [n, 1] }] | |
| optimal_solution = [] | |
| until solutions.empty? | |
| coins = solutions.pop | |
| total = coin_sum(coins) | |
| if total == amount | |
| optimal_solution = coins | |
| elsif (amount - total) >= smallest | |
| new_s = vectors.map { |v| sum(coins, v) }. | |
| reject { |v| visited.key?(v) }. | |
| reject { |v| scores.fetch(coin_sum(v), Float::INFINITY) < v.sum } | |
| solutions += new_s | |
| visited = visited.merge(Hash[new_s.map { |s| [s, true]}]) | |
| scores = scores.merge(Hash[new_s.map { |v| [coin_sum(v), coins.sum] }]) | |
| end | |
| end | |
| Hash[available_coins.zip(optimal_solution)].reject { |k, v| v == 0 } | |
| end | |
| private | |
| def coin_sum(coins) | |
| prod(@available_coins, coins) | |
| end | |
| def prod(a, b) | |
| a.zip(b).reduce(0) { |s, e| s + e.inject(:*) } | |
| end | |
| def sum(a, b) | |
| a.zip(b).reduce([]) { |s, e| s.append(e.sum) } | |
| end | |
| end | |
| # RSPEC Unit Tests: | |
| describe Change do | |
| it "returns [1] for 1" do | |
| expect(subject.change(1)).to eq(1 => 1) | |
| end | |
| it "returns [1, 1, 1, 1] for 4" do | |
| expect(subject.change(4)).to eq(1 => 4) | |
| end | |
| it "returns [5, 1] for 6" do | |
| expect(subject.change(6)).to eq(5 => 1, 1 => 1) | |
| end | |
| it "returns [25, 10, 10, 1, 1, 1] for 48" do | |
| expect(subject.change(48)).to eq(25 => 1, 10 => 2, 1 => 3) | |
| end | |
| it "returns [100, 25, 10, 5, 1, 1] for 142" do | |
| expect(subject.change(142)).to eq(100 => 1, 25 => 1, 10 => 1, 5 => 1, 1 => 2) | |
| end | |
| it "returns [100,100,50,25,10,5,1] for 291" do | |
| expect(subject.change(291)).to eq(100 => 2, 50 => 1, 25 => 1, 10 => 1, 5 => 1, 1 => 1) | |
| end | |
| it "returns [330, 200] for " do | |
| expect(subject.change(530, [500, 330, 250, 200, 167])).to eq(330 => 1, 200 => 1) | |
| end | |
| end |
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