Add problem 1 of chapter 8

src/chapter8/problem1.go

@@ -0,0 +1,28 @@
+package chapter8
+
+// TripleStep calles TripleStepR to calculates possible ways to claim
+func TripleStep(num int) int {
+	if num <= 0 {
+		return 0
+	}
+	memo := make([]int, num+1)
+
+	return TripleStepR(num, memo)
+}
+
+// TripleStepR calculates possible ways to claim give number of stairs with 3, 2, 1 steps
+func TripleStepR(num int, memo []int) int {
+	if num < 0 {
+		return 0
+	} else if num == 0 {
+		return 1
+	}
+
+	if memo[num] == 0 {
+		memo[num] = TripleStepR(num-3, memo) +
+			TripleStepR(num-2, memo) +
+			TripleStepR(num-1, memo)
+	}
+
+	return memo[num]
+}

src/chapter8/problem1_test.go

@@ -0,0 +1,40 @@
+package chapter8
+
+import "testing"
+
+func TestTripleStep(t *testing.T) {
+	tests := map[string]struct {
+		in  int
+		out int
+	}{
+		"Num is 0": {
+			in:  0,
+			out: 0,
+		},
+		"Num is 1": {
+			in:  1,
+			out: 1,
+		},
+		"Num is 2": {
+			in:  2,
+			out: 2,
+		},
+		"Num is 3": {
+			in:  3,
+			out: 4,
+		},
+		"Num is 5": {
+			in:  5,
+			out: 13,
+		},
+	}
+
+	for k, test := range tests {
+		t.Run(k, func(t *testing.T) {
+			out := TripleStep(test.in)
+			if out != test.out {
+				t.Errorf("actual=%d expected=%d", out, test.out)
+			}
+		})
+	}
+}