fannkuch-redux Go program source code

fannkuch-redux.go

package main

import (
    "fmt"
    "os"
    "strconv"
)

func max(a, b int ) int {
    if a > b {
        return a
    }
    return b;
}

func fannkuchredux(n int) int {
    perm := make([]int, n)
    perm1 := make([]int, n)
    count := make([]int, n)
    maxFlipsCount := 0
    permCount := 0;
    checksum := 0;

    for i := 0; i < n; i++ {
        perm1[i] = i
    }
    r := n
    
    for true {
        for r != 1 {
            count[r-1] = r
            r -= 1
        }
        for i := 0; i < n; i += 1 {
            perm[i] = perm1[i]
        }
        flipsCount := 0;

        for k := perm[0]; k != 0; k = perm[0] {
            k2 := (k+1) >> 1
            for i := 0; i < k2; i++ {
                temp := perm[i]
                perm[i] = perm[k-i];
                perm[k-i] = temp
            }
            flipsCount += 1
        }
        
        maxFlipsCount = max(maxFlipsCount, flipsCount)

        csi := flipsCount
        if permCount % 2 != 0 {
            csi = -flipsCount
        }
        checksum += csi
        
        for true {
            if r == n {
                fmt.Printf("%d\n", checksum)
                return maxFlipsCount
            }
        
            perm0 := perm1[0]
            i := 0;
            for i < r {
                j := i + 1;
                perm1[i] = perm1[j]
                i = j
            }
            perm1[r] = perm0
            count[r] = count[r] - 1
            if count[r] > 0 {
                break
            }
            r++;
        }
        permCount++;
    }    
    return 0;
}

func main() {
    n := 7
    if len(os.Args) > 1 {
        v, err := strconv.Atoi(os.Args[1])
        if err != nil {
            fmt.Printf( "error: %s\n", err.String() )
            return
        }
        n = v
    }    
    
    fmt.Printf("Pfannkuchen(%d) = %d\n", n, fannkuchredux(n));
}