2-B-1, 2-B-2

2-B-2/main_test.go

@@ -0,0 +1,61 @@
+package algo
+
+import (
+	"math/rand"
+	"testing"
+)
+
+func TestDPKnownCase(t *testing.T) {
+	arr := []int{30, 35, 15, 5, 10, 20, 25}
+	want := 15125
+
+	if got := DP(arr); got != want {
+		t.Fatalf("DP(%v) = %d, want %d", arr, got, want)
+	}
+}
+
+func TestGreedyRandomCompare(t *testing.T) {
+	r := rand.New(rand.NewSource(1))
+
+	for tc := 0; tc < 500; tc++ {
+		matrixCount := r.Intn(5) + 3
+		arr := make([]int, matrixCount+1)
+		for i := range arr {
+			arr[i] = r.Intn(9) + 2
+		}
+
+		greedy := Greedy(arr)
+		dp := DP(arr)
+		if greedy < dp {
+			t.Fatalf("greedy beat dp unexpectedly: arr=%v greedy=%d dp=%d", arr, greedy, dp)
+		}
+	}
+}
+
+func TestGreedyIsNotAlwaysOptimal(t *testing.T) {
+	r := rand.New(rand.NewSource(2))
+	found := false
+
+	for tc := 0; tc < 500; tc++ {
+		matrixCount := r.Intn(5) + 3
+		arr := make([]int, matrixCount+1)
+		for i := range arr {
+			arr[i] = r.Intn(9) + 2
+		}
+
+		greedy := Greedy(arr)
+		dp := DP(arr)
+		if dp < greedy {
+			t.Logf("found counterexample: arr=%v greedy=%d dp=%d", arr, greedy, dp)
+			found = true
+		}
+
+		if dp > greedy {
+			t.Fatalf("why greedy < dp???")
+		}
+	}
+
+	if !found {
+		t.Fatal("expected to find at least one case where dp < greedy")
+	}
+}