Add an iterative rational implementation for exact results

.gitignore

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+# Build go binary
+
+frog

README.md

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 # frog_problem
 Here is the frog problem code I wrote in an Edinburgh pub.
 
-Feel free to make better version. This one has not changed since I wrote it. V1 was the same code but saved before I changed it to work for different distances so I have not bothered upload it as well (it was still very unifinished).
+Feel free to make better version. This one has not changed since I wrote it. V1
+was the same code but saved before I changed it to work for different distances
+so I have not bothered upload it as well (it was still very unifinished).
 
-Video is here: https://youtu.be/ZLTyX4zL2Fc
+Video is here: https://youtu.be/ZLTyX4zL2Fc

go.mod

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+module github.com/standupmaths/frog
+
+go 1.12

main.go

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+package main
+
+import (
+	"fmt"
+	"math/big"
+	"os"
+	"strconv"
+)
+
+func main() {
+	// Parse input value from command line args.  Do simple validation.
+	n := 10
+	if len(os.Args) > 1 {
+		parsed, err := strconv.ParseInt(os.Args[1], 10, 64)
+		if err != nil || parsed < 1 {
+			panic("Input target must be a positive integer")
+		}
+		n = int(parsed)
+	}
+
+	sum := big.NewRat(0, 1)
+
+	for i := 1; i <= n; i++ {
+		sum = sum.Add(sum, big.NewRat(1, int64(i)))
+	}
+
+	fmt.Printf("Frog(%d) = %s == %s\n", n, sum.String(), sum.FloatString(10))
+}