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# esimov/factorial.go

Last active June 11, 2023 21:19
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Factorial calculation in Go lang using three different methods: first traditionally, second with closure and third using memoization. The last method is the fastest between the three.
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 package main import ( "fmt" "time" ) const LIM = 41 var facts [LIM]uint64 func main() { fmt.Println("==================FACTORIAL==================") start := time.Now() for i:=uint64(0); i < LIM; i++ { fmt.Printf("Factorial for %d is : %d \n", i, Factorial(uint64(i))) } end := time.Now() fmt.Printf("Calculation finished in %s \n", end.Sub(start)) //Calculation finished in 2.0002ms fmt.Println("==================FACTORIAL CLOSURE==================") start = time.Now() fact := FactorialClosure() for i:=uint64(0); i < LIM; i++ { fmt.Printf("Factorial closure for %d is : %d \n", uint64(i), fact(uint64(i))) } end = time.Now() fmt.Printf("Calculation finished in %s \n", end.Sub(start)) //Calculation finished in 1ms fmt.Println("==================FACTORIAL MEMOIZATION==================") start = time.Now() var result uint64 = 0 for i:=uint64(0); i < LIM; i++ { result = FactorialMemoization(uint64(i)) fmt.Printf("The factorial value for %d is %d\n", uint64(i), uint64(result)) } end = time.Now() fmt.Printf("Calculation finished in %s\n", end.Sub(start)) // Calculation finished in 0ms } func Factorial(n uint64)(result uint64) { if (n > 0) { result = n * Factorial(n-1) return result } return 1 } func FactorialClosure() func(n uint64)(uint64) { var a,b uint64 = 1, 1 return func(n uint64)(uint64) { if (n > 1) { a, b = b, uint64(n) * uint64(b) } else { return 1 } return b } } func FactorialMemoization(n uint64)(res uint64) { if (facts[n] != 0) { res = facts[n] return res } if (n > 0) { res = n * FactorialMemoization(n-1) return res } return 1 }

### slava-nikulin commented Jun 11, 2023

FactorialMemoization is not correct. If you want to use DP way, you need to fill facts array. But technically it will not has any differences with regular recursion