left right bound

Author: kimi0230

Leetcode/0704.Binary-Search/main.go

@@ -85,3 +85,62 @@ func BinarySearchRecursively(nums []int, target int, start int, end int) int {
 		return BinarySearchRecursively(nums, target, start, middle-1)
 	}
 }
+
+// 有點類似 nums 小於 target的元素有幾個
+func LeftBound(nums []int, target int) (index int) {
+	lenght := len(nums)
+	if lenght <= 0 {
+		return -1
+	}
+	left, right := 0, lenght-1
+
+	for left <= right {
+		// 除以2
+		// mid := left + (right-left)>>1
+		mid := int(uint(right+left) >> 1)
+		if nums[mid] == target {
+			// 要繼續找左邊, 所以把右邊變小
+			right = mid - 1
+		} else if nums[mid] < target {
+			// 找右邊
+			left = mid + 1
+		} else if nums[mid] > target {
+			// 找左邊
+			right = mid - 1
+		}
+	}
+	// 都沒找到 注意: left越界情況
+	if left >= lenght || nums[left] != target {
+		return -1
+	}
+	return left
+}
+
+func RightBound(nums []int, target int) (index int) {
+	lenght := len(nums)
+	if lenght <= 0 {
+		return -1
+	}
+	left, right := 0, lenght-1
+
+	for left <= right {
+		// 除以2
+		// mid := left + (right-left)>>1
+		mid := int(uint(right+left) >> 1)
+		if nums[mid] == target {
+			// 注意:要繼續找右邊, 所以把左邊變大=mid+1
+			left = mid + 1
+		} else if nums[mid] < target {
+			// 找右邊
+			left = mid + 1
+		} else if nums[mid] > target {
+			// 找左邊
+			right = mid - 1
+		}
+	}
+	// 都沒找到 注意:right越界情況
+	if right < 0 || nums[right] != target {
+		return -1
+	}
+	return right
+}

Leetcode/0704.Binary-Search/main_test.go

@@ -24,6 +24,50 @@ var tests = []struct {
 	},
 }
 
+var leftboundtests = []struct {
+	arg1 []int
+	arg2 int
+	want int
+}{
+	{
+		[]int{1, 2, 2, 2, 3},
+		2,
+		1,
+	},
+	{
+		[]int{2, 3, 5, 7},
+		1,
+		-1,
+	},
+	{
+		[]int{2, 3, 5, 7},
+		8,
+		-1,
+	},
+}
+
+var rightboundtests = []struct {
+	arg1 []int
+	arg2 int
+	want int
+}{
+	{
+		[]int{1, 2, 2, 4},
+		2,
+		2,
+	},
+	{
+		[]int{1, 2, 2, 4},
+		0,
+		-1,
+	},
+	{
+		[]int{2, 3, 5, 7},
+		7,
+		3,
+	},
+}
+
 func TestSearch(t *testing.T) {
 	for _, tt := range tests {
 		if got := Search(tt.arg1, tt.arg2); got != tt.want {
@@ -40,6 +84,22 @@ func TestSearch2(t *testing.T) {
 	}
 }
 
+func TestLeftBound(t *testing.T) {
+	for _, tt := range leftboundtests {
+		if got := LeftBound(tt.arg1, tt.arg2); got != tt.want {
+			t.Errorf("got = %v, want = %v", got, tt.want)
+		}
+	}
+}
+
+func TestRightBound(t *testing.T) {
+	for _, tt := range rightboundtests {
+		if got := RightBound(tt.arg1, tt.arg2); got != tt.want {
+			t.Errorf("got = %v, want = %v", got, tt.want)
+		}
+	}
+}
+
 func TestBinarySearch(t *testing.T) {
 	for _, tt := range tests {
 		if got := BinarySearch(tt.arg1, tt.arg2); got != tt.want {