From c1a688bf2f45c96e7ce4f296e75d5bd66b51d06b Mon Sep 17 00:00:00 2001
From: Matej Focko <mfocko@redhat.com>
Date: Thu, 20 Jan 2022 20:49:44 +0100
Subject: [PATCH] dynamic-programming(i): add day 2 and rename day 1

Signed-off-by: Matej Focko <mfocko@redhat.com>
---
 .../{day-1 => day-01}/fibonacci-number.rb     |  0
 .../{day-1 => day-01}/tribonacci.rb           |  0
 .../day-02/climbing-stairs.rb                 | 27 ++++++++++++++++++
 .../day-02/min-cost-climbing-stairs.rb        | 28 +++++++++++++++++++
 4 files changed, 55 insertions(+)
 rename study-plan/dynamic-programming/{day-1 => day-01}/fibonacci-number.rb (100%)
 rename study-plan/dynamic-programming/{day-1 => day-01}/tribonacci.rb (100%)
 create mode 100644 study-plan/dynamic-programming/day-02/climbing-stairs.rb
 create mode 100644 study-plan/dynamic-programming/day-02/min-cost-climbing-stairs.rb

diff --git a/study-plan/dynamic-programming/day-1/fibonacci-number.rb b/study-plan/dynamic-programming/day-01/fibonacci-number.rb
similarity index 100%
rename from study-plan/dynamic-programming/day-1/fibonacci-number.rb
rename to study-plan/dynamic-programming/day-01/fibonacci-number.rb
diff --git a/study-plan/dynamic-programming/day-1/tribonacci.rb b/study-plan/dynamic-programming/day-01/tribonacci.rb
similarity index 100%
rename from study-plan/dynamic-programming/day-1/tribonacci.rb
rename to study-plan/dynamic-programming/day-01/tribonacci.rb
diff --git a/study-plan/dynamic-programming/day-02/climbing-stairs.rb b/study-plan/dynamic-programming/day-02/climbing-stairs.rb
new file mode 100644
index 0000000..a52586e
--- /dev/null
+++ b/study-plan/dynamic-programming/day-02/climbing-stairs.rb
@@ -0,0 +1,27 @@
+# @param {Integer} n
+# @return {Integer}
+def climb_stairs(n)
+    possible_ways = [0, 1, 2]
+
+    k = 3
+    while possible_ways.size <= n do
+        possible_ways.push(possible_ways[k - 1] + possible_ways[k - 2])
+        k += 1
+    end
+
+    return possible_ways[n]
+end
+
+RSpec.describe "climb_stairs" do
+    it "1 is 1" do
+        expect(climb_stairs(1)).to eq(1)
+    end
+
+    it "2 is 2" do
+        expect(climb_stairs(2)).to eq(2)
+    end
+
+    it "3 is 3" do
+        expect(climb_stairs(3)).to eq(3)
+    end
+end
diff --git a/study-plan/dynamic-programming/day-02/min-cost-climbing-stairs.rb b/study-plan/dynamic-programming/day-02/min-cost-climbing-stairs.rb
new file mode 100644
index 0000000..01ac4f2
--- /dev/null
+++ b/study-plan/dynamic-programming/day-02/min-cost-climbing-stairs.rb
@@ -0,0 +1,28 @@
+# @param {Integer[]} cost
+# @return {Integer}
+def min_cost_climbing_stairs(cost)
+    def get(cost, k)
+        if k < 0 || k >= cost.size then
+            return 0
+        end
+        return cost[k]
+    end
+
+    i = cost.size - 1
+    while i >= 0 do
+        cost[i] += [get(cost, i + 1), get(cost, i + 2)].min
+        i -= 1
+    end
+
+    return cost.take(2).min
+end
+
+RSpec.describe "min_cost_climbing_stairs" do
+    it "of [10,15,20] is 15" do
+        expect(min_cost_climbing_stairs([10,15,20])).to eq(15)
+    end
+
+    it "of [1,100,1,1,1,100,1,1,100,1] is 6" do
+        expect(min_cost_climbing_stairs([1,100,1,1,1,100,1,1,100,1])).to eq(6)
+    end
+end