sort: add examples for sort.Search

This adds examples showing the different ways of using sort.Search.

Change-Id: Iaa08b4501691f37908317fdcf2e618fbe9f99ade
Reviewed-on: https://go-review.googlesource.com/29131Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/sort/example_search_test.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sort_test
+
+import (
+	"fmt"
+	"sort"
+)
+
+// This example demonstrates searching a list sorted in ascending order.
+func ExampleSearch() {
+	a := []int{1, 3, 6, 10, 15, 21, 28, 36, 45, 55}
+	x := 6
+
+	i := sort.Search(len(a), func(i int) bool { return a[i] >= x })
+	if i < len(a) && a[i] == x {
+		fmt.Printf("found %d at index %d in %v\n", x, i, a)
+	} else {
+		fmt.Printf("%d not found in %v\n", x, a)
+	}
+	// Output:
+	// found 6 at index 2 in [1 3 6 10 15 21 28 36 45 55]
+}
+
+// This example demonstrates searching a list sorted in descending order.
+// The approach is the same as searching a list in ascending order,
+// but with the condition inverted.
+func ExampleSearch_descendingOrder() {
+	a := []int{55, 45, 36, 28, 21, 15, 10, 6, 3, 1}
+	x := 6
+
+	i := sort.Search(len(a), func(i int) bool { return a[i] <= x })
+	if a[i] == x {
+		fmt.Printf("found %d at index %d in %v\n", x, i, a)
+	} else {
+		fmt.Printf("%d not found in %v\n", x, a)
+	}
+	// Output:
+	// found 6 at index 7 in [55 45 36 28 21 15 10 6 3 1]
+}