2.3-7

Author: jeffmingup

exercises/2.3-7.go

@@ -0,0 +1,33 @@
+package exercises
+
+import (
+	"arithmetic/sort"
+)
+
+func SearchSum(arr []int, sum int) bool {
+	sort.MergeSort(arr, 0, len(arr)-1) //归并排序 O(n lgn) 复杂度
+	if arr[0] > sum {
+		return false
+	}
+	for i := 0; i < len(arr)-1; i++ { //n次循环 加二分查找 也是 O(n lgn) 复杂度
+		ret := binarySearch(arr[i+1:], sum-arr[i])
+		if ret != -1 {
+			return true
+		}
+	}
+	return false
+}
+func binarySearch(arr []int, key int) int {
+	start, end := 0, len(arr)-1
+	for start <= end {
+		mid := start + (end-start)/2
+		if key > arr[mid] {
+			start = mid + 1
+		} else if key < arr[mid] {
+			end = mid - 1
+		} else {
+			return mid
+		}
+	}
+	return -1
+}

exercises/2.3-7_test.go

@@ -0,0 +1,12 @@
+package exercises
+
+import (
+	"testing"
+)
+
+func TestSearchSum(t *testing.T) {
+	arr := []int{5, 7, 3, 2, 7, 55, 33, 55, 13, 56, 758}
+	if !SearchSum(arr, 8) {
+		t.Fail()
+	}
+}

sort/insert_sort.go

@@ -32,6 +32,7 @@ func InsertSort2(arr []int) {
 
 }
 
+//二分查找递归版
 func suitableIndex(list []int, start int, end int, current int) int {
 	// 比到最后没的比的时候就去对比下当前位置与待排元素的大小，并返回较大值的位置
 	if start >= end {
@@ -52,6 +53,8 @@ func suitableIndex(list []int, start int, end int, current int) int {
 	}
 
 }
+
+//二分查找循环版
 func suitableIndex2(list []int) int {
 	key := len(list) - 1
 	start, end := 0, len(list)-2