binary search

binarysearch/binarysearch.go

@@ -0,0 +1,36 @@
+package binarysearch
+
+import "sort"
+
+func search(nums []int, target int) int {
+	start := 0
+	end := len(nums) - 1
+	for start <= end {
+		mid := (start + end) / 2
+		if nums[mid] == target {
+			return mid
+		} else if nums[mid] > target {
+			end = mid - 1
+		} else if nums[mid] < target {
+			start = mid + 1
+		}
+	}
+
+	return -1
+}
+
+func Search(nums []int, target int) int {
+	return search(nums, target)
+}
+
+// Uses sort.SearchInts
+func SearchStdLib(nums []int, target int) int {
+	idx, found := sort.Find(len(nums), func(i int) int {
+		return target - nums[i]
+	})
+
+	if found {
+		return idx
+	}
+	return -1
+}

binarysearch/binarysearch_test.go

@@ -0,0 +1,39 @@
+package binarysearch_test
+
+import (
+	"testing"
+
+	bs "git.jxs.me/leetgo/binarysearch"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEmpty(t *testing.T) {
+	require.Equal(t, -1, bs.Search([]int{}, 7))
+}
+
+func TestSingle(t *testing.T) {
+	require.Equal(t, 0, bs.Search([]int{6}, 6))
+}
+
+func TestTwo(t *testing.T) {
+	require.Equal(t, -1, bs.Search([]int{2, 5}, 0))
+}
+
+func TestMulti(t *testing.T) {
+	require.Equal(t, 5, bs.Search([]int{1, 2, 3, 4, 5, 6, 7}, 6))
+}
+func TestMultiEnd(t *testing.T) {
+	require.Equal(t, 6, bs.Search([]int{1, 2, 3, 4, 5, 6, 7}, 7))
+}
+
+func TestMultiStart(t *testing.T) {
+	require.Equal(t, 0, bs.Search([]int{1, 2, 3, 4, 5, 6, 7}, 1))
+}
+
+func TestExample1(t *testing.T) {
+	require.Equal(t, 4, bs.Search([]int{-1, 0, 3, 5, 9, 12}, 9))
+}
+
+func TestExample2(t *testing.T) {
+	require.Equal(t, -1, bs.Search([]int{-1, 0, 3, 5, 9, 12}, 2))
+}

binarysearch/readme.md

@@ -0,0 +1,29 @@
+704. Binary Search
+Easy
+
+Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.
+
+You must write an algorithm with O(log n) runtime complexity.
+
+ 
+
+Example 1:
+
+Input: nums = [-1,0,3,5,9,12], target = 9
+Output: 4
+Explanation: 9 exists in nums and its index is 4
+
+Example 2:
+
+Input: nums = [-1,0,3,5,9,12], target = 2
+Output: -1
+Explanation: 2 does not exist in nums so return -1
+
+ 
+
+Constraints:
+
+    1 <= nums.length <= 104
+    -104 < nums[i], target < 104
+    All the integers in nums are unique.
+    nums is sorted in ascending order.