whatcanGOwrong

go/pkg/mod/golang.org/x/exp@v0.0.0-20230224173230-c95f2b4c22f2/shootout/fannkuch.go

@@ -0,0 +1,125 @@
+//go:build ignore
+// +build ignore
+
+/*
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in the
+    documentation and/or other materials provided with the distribution.
+
+    * Neither the name of "The Computer Language Benchmarks Game" nor the
+    name of "The Computer Language Shootout Benchmarks" nor the names of
+    its contributors may be used to endorse or promote products derived
+    from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+*/
+
+/*
+ * The Computer Language Benchmarks Game
+ * http://shootout.alioth.debian.org/
+ *
+ * contributed by The Go Authors.
+ * Based on fannkuch.c by Heiner Marxen
+ */
+
+package main
+
+import (
+	"flag"
+	"fmt"
+)
+
+var n = flag.Int("n", 7, "count")
+
+func fannkuch(n int) int {
+	if n < 1 {
+		return 0
+	}
+
+	n1 := n - 1
+	perm := make([]int, n)
+	perm1 := make([]int, n)
+	count := make([]int, n)
+
+	for i := 0; i < n; i++ {
+		perm1[i] = i // initial (trivial) permutation
+	}
+
+	r := n
+	didpr := 0
+	flipsMax := 0
+	for {
+		if didpr < 30 {
+			for i := 0; i < n; i++ {
+				fmt.Printf("%d", 1+perm1[i])
+			}
+			fmt.Printf("\n")
+			didpr++
+		}
+		for ; r != 1; r-- {
+			count[r-1] = r
+		}
+
+		if perm1[0] != 0 && perm1[n1] != n1 {
+			flips := 0
+			for i := 1; i < n; i++ { // perm = perm1
+				perm[i] = perm1[i]
+			}
+			k := perm1[0] // cache perm[0] in k
+			for {         // k!=0 ==> k>0
+				for i, j := 1, k-1; i < j; i, j = i+1, j-1 {
+					perm[i], perm[j] = perm[j], perm[i]
+				}
+				flips++
+				// Now exchange k (caching perm[0]) and perm[k]... with care!
+				j := perm[k]
+				perm[k] = k
+				k = j
+				if k == 0 {
+					break
+				}
+			}
+			if flipsMax < flips {
+				flipsMax = flips
+			}
+		}
+
+		for ; r < n; r++ {
+			// rotate down perm[0..r] by one
+			perm0 := perm1[0]
+			for i := 0; i < r; i++ {
+				perm1[i] = perm1[i+1]
+			}
+			perm1[r] = perm0
+			count[r]--
+			if count[r] > 0 {
+				break
+			}
+		}
+		if r == n {
+			return flipsMax
+		}
+	}
+	return 0
+}
+
+func main() {
+	flag.Parse()
+	fmt.Printf("Pfannkuchen(%d) = %d\n", *n, fannkuch(*n))
+}