chore: multiply strings

Author: lupppig

multiply_string.go

@@ -0,0 +1,131 @@
+package main
+
+import (
+	"fmt"
+)
+
+/*
+*
+Given two non-negative integers num1 and num2 represented as strings,
+return the product of num1 and num2, also represented as a string.
+Note: You must not use any built-in BigInteger library or convert the inputs to integer directly.
+*/
+
+// worst case could cause integer overflow...
+// O(n)
+// for int 64
+// 498828660196 * 498828660196 = -3269442614257959980 // integer overflow right here
+func Multiply(num1 string, num2 string) string {
+	strMap := map[string]int{
+		"0": 0,
+		"1": 1,
+		"2": 2,
+		"3": 3,
+		"4": 4,
+		"5": 5,
+		"6": 6,
+		"7": 7,
+		"8": 8,
+		"9": 9,
+	}
+	var va int64
+	var vap int64
+
+	num1Len := len(num1)
+	num2Len := len(num2)
+
+	i, j := 0, 0
+
+	for i < num1Len || j < num2Len {
+		if i < num1Len {
+			va = va*10 + int64(strMap[string(num1[i])])
+		}
+		if j < num2Len {
+			vap = vap*10 + int64(strMap[string(num2[j])])
+		}
+		i++
+		j++
+	}
+	return fmt.Sprintf("%d", va*vap)
+}
+
+func Multiply2(num1 string, num2 string) string {
+
+	if num1 == "0" || num2 == "0" {
+		return "0"
+	}
+
+	n, m := len(num1), len(num2)
+	result := make([]int, n+m)
+	for i := n - 1; i >= 0; i-- {
+		for j := m - 1; j >= 0; j-- {
+			d1 := int(num1[i] - '0')
+			d2 := int(num2[j] - '0')
+			mul := d1 * d2
+			p1, p2 := i+j, i+j+1
+			sum := mul + result[p2]
+			result[p2] = sum % 10
+			result[p1] += sum / 10
+		}
+	}
+	res := ""
+	for _, digit := range result {
+		if !(len(res) == 0 && digit == 0) {
+			res += fmt.Sprint(digit)
+		}
+	}
+	return res
+}
+
+func main() {
+	fmt.Println(Multiply2("498828660196", "840477629533"))
+}
+
+/*
+*
+
+	apparently this function is illegal to use
+	sybau...
+*/
+func convertToInt(str string) int {
+	if str == "" || str == " " || len(str) == 0 {
+		return 0
+	}
+
+	num := 0
+	sign := 1
+
+	if str[0] == '-' {
+		sign = -1
+		str = str[1:]
+	}
+
+	for _, c := range str {
+		switch c {
+		case '0':
+			num = (num * 10)
+		case '1':
+			num = (num * 10) + 1
+		case '2':
+			num = (num * 10) + 2
+		case '3':
+			num = (num * 10) + 3
+		case '4':
+			num = (num * 10) + 4
+		case '5':
+			num = (num * 10) + 5
+		case '6':
+			num = (num * 10) + 6
+		case '7':
+			num = (num * 10) + 7
+		case '8':
+			num = (num * 10) + 8
+		case '9':
+			num = (num * 10) + 9
+		default:
+			fmt.Println("bleh bleh bleeeeh bleeeeeeeeeeeh")
+			return 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 // don't ask me why this here...
+		}
+	}
+	return num * sign
+}

multiply_string_test.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestMultiply(t *testing.T) {
+
+	var additiveTest = []struct {
+		a      string
+		b      string
+		expect string
+	}{
+		{
+			a:      "1",
+			b:      "2",
+			expect: "2",
+		},
+		{
+			a:      "123",
+			b:      "456",
+			expect: "56088",
+		},
+		{
+			a:      "498828660196",
+			b:      "840477629533",
+			expect: "419254329864656431168468",
+		},
+	}
+
+	for _, mul := range additiveTest {
+		got := Multiply2(mul.a, mul.b)
+		if mul.expect != got {
+			t.Errorf("expected %s got %s in test multiply string", mul.expect, got)
+		}
+
+	}
+}

two_numbers.go

@@ -68,35 +68,35 @@ func (l *ListNode) PrintNode() {
 	fmt.Println()
 }
 
-func main() {
-	node2 := Node{}
-	Lnn := &ListNode{Val: 9}
-	Lnn1 := &ListNode{Val: 9}
-	Lnn2 := &ListNode{Val: 9}
-	Lnn3 := &ListNode{Val: 9}
-	Lnn4 := &ListNode{Val: 9}
-	Lnn5 := &ListNode{Val: 9}
-	Lnn6 := &ListNode{Val: 9}
+// func main() {
+// 	node2 := Node{}
+// 	Lnn := &ListNode{Val: 9}
+// 	Lnn1 := &ListNode{Val: 9}
+// 	Lnn2 := &ListNode{Val: 9}
+// 	Lnn3 := &ListNode{Val: 9}
+// 	Lnn4 := &ListNode{Val: 9}
+// 	Lnn5 := &ListNode{Val: 9}
+// 	Lnn6 := &ListNode{Val: 9}
 
-	node2.Prepend(Lnn)
-	node2.Prepend(Lnn1)
-	node2.Prepend(Lnn2)
-	node2.Prepend(Lnn3)
-	node2.Prepend(Lnn4)
-	node2.Prepend(Lnn5)
-	node2.Prepend(Lnn6)
+// 	node2.Prepend(Lnn)
+// 	node2.Prepend(Lnn1)
+// 	node2.Prepend(Lnn2)
+// 	node2.Prepend(Lnn3)
+// 	node2.Prepend(Lnn4)
+// 	node2.Prepend(Lnn5)
+// 	node2.Prepend(Lnn6)
 
-	node := Node{}
-	Ln := &ListNode{Val: 9}
-	Ln1 := &ListNode{Val: 9}
-	Ln2 := &ListNode{Val: 9}
-	Ln3 := &ListNode{Val: 9}
+// 	node := Node{}
+// 	Ln := &ListNode{Val: 9}
+// 	Ln1 := &ListNode{Val: 9}
+// 	Ln2 := &ListNode{Val: 9}
+// 	Ln3 := &ListNode{Val: 9}
 
-	node.Prepend(Ln)
-	node.Prepend(Ln1)
-	node.Prepend(Ln2)
-	node.Prepend(Ln3)
+// 	node.Prepend(Ln)
+// 	node.Prepend(Ln1)
+// 	node.Prepend(Ln2)
+// 	node.Prepend(Ln3)
 
-	a := addTwoNumbers(node2.Head, node.Head)
-	a.PrintNode()
-}
+// 	a := addTwoNumbers(node2.Head, node.Head)
+// 	a.PrintNode()
+// }