dynamic-programming(i): add day 2 and rename day 1

Signed-off-by: Matej Focko <mfocko@redhat.com>

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

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