finish Problem 34

Author: aQua

Algorithms/0034.search-for-a-range/README.md

@@ -1,10 +1,18 @@
 # [34. Search for a Range](https://leetcode.com/problems/search-for-a-range/)
 
 ## 题目
+Given an array of integers sorted in ascending order, find the starting and ending position of a given target value.
 
+Your algorithm's runtime complexity must be in the order of O(log n).
 
-## 解题思路
+If the target is not found in the array, return [-1, -1].
+
+For example,
+Given [5, 7, 7, 8, 8, 10] and target value 8,
+return [3, 4].
 
+## 解题思路
+见注释
 
 ## 总结
 

Algorithms/0034.search-for-a-range/search-for-a-range.go

@@ -1,2 +1,52 @@
 package Problem0034
 
+func searchRange(nums []int, target int) []int {
+	// 查看target是否存在与nums中
+	index := search(nums, target)
+	if index == -1 {
+		return []int{-1, -1}
+	}
+
+	// 利用二分法，查找第一个target
+	first := index
+	for {
+		f := search(nums[:first], target)
+		if f == -1 {
+			break
+		}
+		first = f
+	}
+
+	// 利用二分法，查找最后一个target
+	last := index
+	for {
+		l := search(nums[last+1:], target)
+		if l == -1 {
+			break
+		}
+		// 注意这里与查找first的不同
+		last += l + 1
+	}
+
+	return []int{first, last}
+}
+
+// 二分查找法
+func search(nums []int, target int) int {
+	low, high := 0, len(nums)-1
+	var median int
+
+	for low <= high {
+		median = (low + high) / 2
+
+		switch {
+		case nums[median] < target:
+			low = median + 1
+		case nums[median] > target:
+			high = median - 1
+		default:
+			return median
+		}
+	}
+	return -1
+}

Algorithms/0034.search-for-a-range/search-for-a-range_test.go

@@ -1,8 +1,8 @@
 package Problem0034
 
 import (
-	"testing"
 	"fmt"
+	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -15,13 +15,14 @@ type question struct {
 // para 是参数
 // one 代表第一个参数
 type para struct {
-	one string
+	one []int
+	two int
 }
 
 // ans 是答案
 // one 代表第一个答案
 type ans struct {
-	one string
+	one []int
 }
 
 func Test_Problem0034(t *testing.T) {
@@ -30,17 +31,27 @@ func Test_Problem0034(t *testing.T) {
 	qs := []question{
 
 		question{
-			para{""},
-			ans{""},
+			para{[]int{5, 7, 7, 8, 8, 10}, 8},
+			ans{[]int{3, 4}},
+		},
+
+		question{
+			para{[]int{5, 7, 7, 8, 8, 10}, 6},
+			ans{[]int{-1, -1}},
 		},
-	
+
+		question{
+			para{[]int{5, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 10}, 8},
+			ans{[]int{3, 12}},
+		},
+
 		// 如需多个测试，可以复制上方元素。
 	}
 
 	for _, q := range qs {
 		a, p := q.ans, q.para
 		fmt.Printf("~~%v~~\n", p)
 
-		ast.Equal(a.one, (p.one), "输入:%v", p)
+		ast.Equal(a.one, searchRange(p.one, p.two), "输入:%v", p)
 	}
 }