chore: save day18 (#12)

Reviewed-on: #12

math.go

@@ -0,0 +1,96 @@
+package aoc
+
+import "cmp"
+
+type uinteger interface {
+	uint | uint8 | uint16 | uint32 | uint64
+}
+type sinteger interface {
+	int | int8 | int16 | int32 | int64
+}
+type integer interface {
+	sinteger | uinteger
+}
+
+// type float interface {
+// 	complex64 | complex128 | float32 | float64
+// }
+// type number interface{ integer | float }
+
+// greatest common divisor (GCD) via Euclidean algorithm
+func GCD[T integer](a, b T) T {
+	for b != 0 {
+		t := b
+		b = a % b
+		a = t
+	}
+	return a
+}
+
+// find Least Common Multiple (LCM) via GCD
+func LCM[T integer](integers ...T) T {
+	if len(integers) == 0 {
+		return 0
+	}
+	if len(integers) == 1 {
+		return integers[0]
+	}
+
+	a, b := integers[0], integers[1]
+	result := a * b / GCD(a, b)
+
+	for _, c := range integers[2:] {
+		result = LCM(result, c)
+	}
+
+	return result
+}
+
+func Sum[T integer](arr ...T) T {
+	var acc T
+	for _, a := range arr {
+		acc += a
+	}
+	return acc
+}
+func SumFunc[T any, U integer](fn func(T) U, input ...T) U {
+	return Sum(SliceMap(fn, input...)...)
+}
+func SumIFunc[T any, U integer](fn func(int, T) U, input ...T) U {
+	return Sum(SliceIMap(fn, input...)...)
+}
+
+func Power2(n int) int {
+	if n == 0 {
+		return 1
+	}
+	p := 2
+	for ; n > 1; n-- {
+		p *= 2
+	}
+	return p
+}
+
+func ABS(i int) int {
+	if i < 0 {
+		return -i
+	}
+	return i
+}
+
+func Max[T cmp.Ordered](a T, v ...T) T {
+	for _, b := range v {
+		if b > a {
+			a = b
+		}
+	}
+	return a
+}
+func Min[T cmp.Ordered](a T, v ...T) T {
+	for _, b := range v {
+		if b < a {
+			a = b
+		}
+	}
+	return a
+}