From dfbb9e30e04d6b3d8a9cc074ab7a47bd4d54070d Mon Sep 17 00:00:00 2001
From: dudaodong <lanliddd.2007@163.com>
Date: Mon, 17 Jan 2022 15:36:48 +0800
Subject: [PATCH] feat: algorithm package, BinarySearch and
 BinaryIterativeSearch functions

---
 algorithm/search.go      | 45 ++++++++++++++++++++++++++++++++++++++++
 algorithm/search_test.go | 25 ++++++++++++++++++++++
 2 files changed, 70 insertions(+)
 create mode 100644 algorithm/search.go
 create mode 100644 algorithm/search_test.go

diff --git a/algorithm/search.go b/algorithm/search.go
new file mode 100644
index 0000000..ad7a533
--- /dev/null
+++ b/algorithm/search.go
@@ -0,0 +1,45 @@
+// Copyright 2021 dudaodong@gmail.com. All rights reserved.
+// Use of this source code is governed by MIT license
+
+// Package algorithm contain some basic algorithm functions. eg. sort, search, list, linklist, stack, queue, tree, graph. TODO
+package algorithm
+
+import "github.com/duke-git/lancet/lancetconstraints"
+
+// BinarySearch search for target within a sorted slice, recursive call itself.
+// If a target is found, the index of the target is returned. Else the function return -1
+func BinarySearch[T any](slice []T, target T, lowIndex, highIndex int, comparator lancetconstraints.Comparator) int {
+	if highIndex < lowIndex || len(slice) == 0 {
+		return -1
+	}
+
+	midIndex := int(lowIndex + (highIndex-lowIndex)/2)
+	// slice[midIndex] > target
+	if comparator.Compare(slice[midIndex], target) == 1 {
+		return BinarySearch(slice, target, lowIndex, midIndex-1, comparator)
+	} else if comparator.Compare(slice[midIndex], target) == -1 {
+		return BinarySearch(slice, target, midIndex+1, highIndex, comparator)
+	}
+
+	return midIndex
+}
+
+// BinaryIterativeSearch search for target within a sorted slice.
+// If a target is found, the index of the target is returned. Else the function return -1
+func BinaryIterativeSearch[T any](slice []T, target T, lowIndex, highIndex int, comparator lancetconstraints.Comparator) int {
+	startIndex := lowIndex
+	endIndex := highIndex
+
+	var midIndex int
+	for startIndex <= endIndex {
+		midIndex = int(startIndex + (endIndex-startIndex)/2)
+		if comparator.Compare(slice[midIndex], target) == 1 {
+			endIndex = midIndex - 1
+		} else if comparator.Compare(slice[midIndex], target) == -1 {
+			startIndex = midIndex + 1
+		} else {
+			return midIndex
+		}
+	}
+	return -1
+}
diff --git a/algorithm/search_test.go b/algorithm/search_test.go
new file mode 100644
index 0000000..340123c
--- /dev/null
+++ b/algorithm/search_test.go
@@ -0,0 +1,25 @@
+package algorithm
+
+import (
+	"testing"
+
+	"github.com/duke-git/lancet/internal"
+)
+
+var sortedNumbers = []int{1, 2, 3, 4, 5, 6, 7, 8}
+
+func TestBinarySearch(t *testing.T) {
+	asssert := internal.NewAssert(t, "TestBinarySearch")
+
+	comparator := &intComparator{}
+	asssert.Equal(4, BinarySearch(sortedNumbers, 5, 0, len(sortedNumbers)-1, comparator))
+	asssert.Equal(-1, BinarySearch(sortedNumbers, 9, 0, len(sortedNumbers)-1, comparator))
+}
+
+func TestBinaryIterativeSearch(t *testing.T) {
+	asssert := internal.NewAssert(t, "TestBinaryIterativeSearch")
+
+	comparator := &intComparator{}
+	asssert.Equal(4, BinaryIterativeSearch(sortedNumbers, 5, 0, len(sortedNumbers)-1, comparator))
+	asssert.Equal(-1, BinaryIterativeSearch(sortedNumbers, 9, 0, len(sortedNumbers)-1, comparator))
+}