move to lib

cmd/partitions.go

@@ -18,46 +18,15 @@ package cmd
 
 import (
 	"fmt"
-	"math/big"
 	"strconv"
 
 	"github.com/spf13/cobra"
+	"scm.dairydemon.net/filifa/mathtools/internal/lib"
 )
 
 var partitionsN string
 var partitionsK string
 
-// given a slice where vals[i] = p_{k-1}(i) for a given k, nextPartition updates the slice so vals[i] = p_k(i) using the property that p_k(n) = p_k(n-k) + p_{k-1}(n)
-func nextPartition(k int, vals []*big.Int) {
-	for i := 1; i < len(vals); i++ {
-		if i-k >= 0 {
-			vals[i].Add(vals[i], vals[i-k])
-		}
-	}
-}
-
-func p(n, k int) *big.Int {
-	if n < 0 {
-		return big.NewInt(0)
-	}
-
-	if k > n {
-		k = n
-	}
-
-	vals := make([]*big.Int, n+1)
-	for i := range vals {
-		vals[i] = big.NewInt(0)
-	}
-	vals[0] = big.NewInt(1)
-
-	for i := 1; i <= k; i++ {
-		nextPartition(i, vals)
-	}
-
-	return vals[n]
-}
-
 func partitions(cmd *cobra.Command, args []string) {
 	n, err := strconv.Atoi(partitionsN)
 	if err != nil {
@@ -83,7 +52,7 @@ func partitions(cmd *cobra.Command, args []string) {
 		cobra.CheckErr("k must be nonnegative")
 	}
 
-	z := p(n, k)
+	z := lib.Partitions(n, k)
 	fmt.Println(z)
 }