good good study, day day up!

vendor/gopl.io/ch4/treesort/sort.go

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+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 101.
+
+// Package treesort provides insertion sort using an unbalanced binary tree.
+package treesort
+
+//!+
+type tree struct {
+	value       int
+	left, right *tree
+}
+
+// Sort sorts values in place.
+func Sort(values []int) {
+	var root *tree
+	for _, v := range values {
+		root = add(root, v)
+	}
+	appendValues(values[:0], root)
+}
+
+// appendValues appends the elements of t to values in order
+// and returns the resulting slice.
+func appendValues(values []int, t *tree) []int {
+	if t != nil {
+		values = appendValues(values, t.left)
+		values = append(values, t.value)
+		values = appendValues(values, t.right)
+	}
+	return values
+}
+
+func add(t *tree, value int) *tree {
+	if t == nil {
+		// Equivalent to return &tree{value: value}.
+		t = new(tree)
+		t.value = value
+		return t
+	}
+	if value < t.value {
+		t.left = add(t.left, value)
+	} else {
+		t.right = add(t.right, value)
+	}
+	return t
+}
+
+//!-

vendor/gopl.io/ch4/treesort/sort_test.go

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+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+package treesort_test
+
+import (
+	"math/rand"
+	"sort"
+	"testing"
+
+	"gopl.io/ch4/treesort"
+)
+
+func TestSort(t *testing.T) {
+	data := make([]int, 50)
+	for i := range data {
+		data[i] = rand.Int() % 50
+	}
+	treesort.Sort(data)
+	if !sort.IntsAreSorted(data) {
+		t.Errorf("not sorted: %v", data)
+	}
+}