Data commit

Task/Calkin-Wilf-sequence/Go/calkin-wilf-sequence.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+    "fmt"
+    "math"
+    "math/big"
+    "strconv"
+    "strings"
+)
+
+func calkinWilf(n int) []*big.Rat {
+    cw := make([]*big.Rat, n+1)
+    cw[0] = big.NewRat(1, 1)
+    one := big.NewRat(1, 1)
+    two := big.NewRat(2, 1)
+    for i := 1; i < n; i++ {
+        t := new(big.Rat).Set(cw[i-1])
+        f, _ := t.Float64()
+        f = math.Floor(f)
+        t.SetFloat64(f)
+        t.Mul(t, two)
+        t.Sub(t, cw[i-1])
+        t.Add(t, one)
+        t.Inv(t)
+        cw[i] = new(big.Rat).Set(t)
+    }
+    return cw
+}
+
+func toContinued(r *big.Rat) []int {
+    a := r.Num().Int64()
+    b := r.Denom().Int64()
+    var res []int
+    for {
+        res = append(res, int(a/b))
+        t := a % b
+        a, b = b, t
+        if a == 1 {
+            break
+        }
+    }
+    le := len(res)
+    if le%2 == 0 { // ensure always odd
+        res[le-1]--
+        res = append(res, 1)
+    }
+    return res
+}
+
+func getTermNumber(cf []int) int {
+    b := ""
+    d := "1"
+    for _, n := range cf {
+        b = strings.Repeat(d, n) + b
+        if d == "1" {
+            d = "0"
+        } else {
+            d = "1"
+        }
+    }
+    i, _ := strconv.ParseInt(b, 2, 64)
+    return int(i)
+}
+
+func commatize(n int) string {
+    s := fmt.Sprintf("%d", n)
+    if n < 0 {
+        s = s[1:]
+    }
+    le := len(s)
+    for i := le - 3; i >= 1; i -= 3 {
+        s = s[0:i] + "," + s[i:]
+    }
+    if n >= 0 {
+        return s
+    }
+    return "-" + s
+}
+
+func main() {
+    cw := calkinWilf(20)
+    fmt.Println("The first 20 terms of the Calkin-Wilf sequnence are:")
+    for i := 1; i <= 20; i++ {
+        fmt.Printf("%2d: %s\n", i, cw[i-1].RatString())
+    }
+    fmt.Println()
+    r := big.NewRat(83116, 51639)
+    cf := toContinued(r)
+    tn := getTermNumber(cf)
+    fmt.Printf("%s is the %sth term of the sequence.\n", r.RatString(), commatize(tn))
+}