good good study, day day up!

vendor/gopl.io/ch4/rev/main.go

@@ -0,0 +1,60 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 86.
+
+// Rev reverses a slice.
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	//!+array
+	a := [...]int{0, 1, 2, 3, 4, 5}
+	reverse(a[:])
+	fmt.Println(a) // "[5 4 3 2 1 0]"
+	//!-array
+
+	//!+slice
+	s := []int{0, 1, 2, 3, 4, 5}
+	// Rotate s left by two positions.
+	reverse(s[:2])
+	reverse(s[2:])
+	reverse(s)
+	fmt.Println(s) // "[2 3 4 5 0 1]"
+	//!-slice
+
+	// Interactive test of reverse.
+	input := bufio.NewScanner(os.Stdin)
+outer:
+	for input.Scan() {
+		var ints []int
+		for _, s := range strings.Fields(input.Text()) {
+			x, err := strconv.ParseInt(s, 10, 64)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err)
+				continue outer
+			}
+			ints = append(ints, int(x))
+		}
+		reverse(ints)
+		fmt.Printf("%v\n", ints)
+	}
+	// NOTE: ignoring potential errors from input.Err()
+}
+
+//!+rev
+// reverse reverses a slice of ints in place.
+func reverse(s []int) {
+	for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
+		s[i], s[j] = s[j], s[i]
+	}
+}
+
+//!-rev