Merge pull request #158 from vaskoz/day74

Day74

README.md

@@ -83,3 +83,4 @@ problems from
 * [Day 71](https://github.com/vaskoz/dailycodingproblem-go/issues/151)
 * [Day 72](https://github.com/vaskoz/dailycodingproblem-go/issues/153)
 * [Day 73](https://github.com/vaskoz/dailycodingproblem-go/issues/155)
+* [Day 74](https://github.com/vaskoz/dailycodingproblem-go/issues/157)

day74/problem.go

@@ -0,0 +1,31 @@
+package day74
+
+// MultiplicationTableBrute counts the number of X occurrences
+// in a N by N multiplication table.
+// Runs in O(N^2) time.
+func MultiplicationTableBrute(N, X int) int {
+	count := 0
+	for i := 1; i <= N; i++ {
+		for j := 1; j <= N; j++ {
+			if i*j == X {
+				count++
+			}
+		}
+	}
+	return count
+}
+
+// MultiplicationTableLinear counts the number of X occurrences
+// in a N by N multiplication table.
+// Runs in O(N) time.
+func MultiplicationTableLinear(N, X int) int {
+	count := 0
+	for i := 1; i <= N; i++ {
+		if i > X {
+			break
+		} else if X%i == 0 && X/i <= N {
+			count++
+		}
+	}
+	return count
+}

day74/problem_test.go

@@ -0,0 +1,48 @@
+package day74
+
+import "testing"
+
+var testcases = []struct {
+	N, X     int
+	expected int
+}{
+	{6, 12, 4},
+	{6, 36, 1},
+	{6, 37, 0},
+	{6, 29, 0},
+	{1000, 29, 2},
+}
+
+func TestMultiplicationTableBrute(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := MultiplicationTableBrute(tc.N, tc.X); result != tc.expected {
+			t.Errorf("Given N=%d X=%d got %d expected %d", tc.N, tc.X, result, tc.expected)
+		}
+	}
+}
+
+func BenchmarkMultiplicationTableBrute(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			MultiplicationTableBrute(tc.N, tc.X)
+		}
+	}
+}
+
+func TestMultiplicationTableLinear(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := MultiplicationTableLinear(tc.N, tc.X); result != tc.expected {
+			t.Errorf("Given N=%d X=%d got %d expected %d", tc.N, tc.X, result, tc.expected)
+		}
+	}
+}
+
+func BenchmarkMultiplicationTableLinear(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			MultiplicationTableLinear(tc.N, tc.X)
+		}
+	}
+}