Merge bb161c2 into 57e41b6

README.md

@@ -97,3 +97,4 @@ problems from
 * [Day 85](https://github.com/vaskoz/dailycodingproblem-go/issues/179)
 * [Day 86](https://github.com/vaskoz/dailycodingproblem-go/issues/181)
 * [Day 87](https://github.com/vaskoz/dailycodingproblem-go/issues/183)
+* [Day 88](https://github.com/vaskoz/dailycodingproblem-go/issues/185)

day88/problem.go

@@ -0,0 +1,64 @@
+package day88
+
+import (
+	"errors"
+)
+
+var errDivideByZero = errors.New("can't divide by zero")
+
+// ErrDivideByZero is the error returned if you attempt to divide by zero.
+func ErrDivideByZero() error {
+	return errDivideByZero
+}
+
+// BruteForceDivision calculates the division by looping subtraction.
+// Runs in O(Quotient) time and O(1) space.
+// Returns an error if divisor is zero.
+func BruteForceDivision(dividend, divisor int32) (int32, error) {
+	if divisor == 0 {
+		return 0, ErrDivideByZero()
+	}
+	negative := (dividend < 0 && divisor > 0) || (dividend >= 0 && divisor < 0)
+	dividend = abs(dividend)
+	divisor = abs(divisor)
+	quotient := int32(0)
+	for dividend >= divisor {
+		dividend -= divisor
+		quotient++
+	}
+	if negative {
+		return -quotient, nil
+	}
+	return quotient, nil
+}
+
+// BitShiftDivision calculates the division by bit-shifting.
+// Runs in O(1) time because it loops over 63-bits and O(1) space.
+// Returns an error if divisor is zero.
+func BitShiftDivision(dividend, divisor int32) (int32, error) {
+	if divisor == 0 {
+		return 0, ErrDivideByZero()
+	}
+	negative := (dividend < 0 && divisor > 0) || (dividend >= 0 && divisor < 0)
+	dividend = abs(dividend)
+	divisor = abs(divisor)
+	var quotient, tmp int64
+	for i := uint(31); i < 32; i-- {
+		if tmp+(int64(divisor)<<i) <= int64(dividend) {
+			tmp += int64(divisor) << i
+			quotient |= int64(1) << i
+		}
+	}
+	if negative {
+		return -int32(quotient), nil
+	}
+	return int32(quotient), nil
+}
+
+// abs returns the absolute value.
+func abs(val int32) int32 {
+	if val < 0 {
+		return -val
+	}
+	return val
+}

day88/problem_test.go

@@ -0,0 +1,47 @@
+package day88
+
+import "testing"
+
+var testcases = []struct {
+	dividend, divisor, quotient int32
+	expectedError               error
+}{
+	{100, 10, 10, nil},
+	{100, -10, -10, nil},
+	{100, 0, 0, ErrDivideByZero()},
+	{1000000, 1, 1000000, nil},
+}
+
+func TestBruteForceDivision(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result, err := BruteForceDivision(tc.dividend, tc.divisor); result != tc.quotient || err != tc.expectedError {
+			t.Errorf("Expected %v,%v got %v,%v", tc.quotient, tc.expectedError, result, err)
+		}
+	}
+}
+
+func BenchmarkBruteForceDivision(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			BruteForceDivision(tc.dividend, tc.divisor)
+		}
+	}
+}
+
+func TestBitShiftDivision(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result, err := BitShiftDivision(tc.dividend, tc.divisor); result != tc.quotient || err != tc.expectedError {
+			t.Errorf("Expected %v,%v got %v,%v", tc.quotient, tc.expectedError, result, err)
+		}
+	}
+}
+
+func BenchmarkBitShiftDivision(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			BitShiftDivision(tc.dividend, tc.divisor)
+		}
+	}
+}