Create binarysearch2.go

16 | 二分查找（下）

go/binarysearch2.go

@@ -0,0 +1,90 @@
+package binarySearch
+
+//查找第一个值等于给定值得元素
+func BinarySearch2(nums []int, value int) int {
+	length := len(nums)
+	start := 0
+	end := length - 1
+	for start <= end {
+		mid := (start + end) / 2
+		if nums[mid] > value {
+			end = mid - 1
+		} else if nums[mid] < value {
+			start = mid + 1
+		} else {
+			for mid >= 0 {
+				if nums[mid-1] == value {
+					mid--
+				} else {
+					return mid
+				}
+			}
+		}
+	}
+	return -1
+}
+
+// 查找最后一个值等于给定值的元素
+func BinarySearch3(nums []int, value int) int {
+	start := 0
+	end := len(nums) - 1
+	for start <= end {
+		mid := (start + end) / 2
+		if nums[mid] > value {
+			end = mid - 1
+		} else if nums[mid] < value {
+			start = mid + 1
+		} else {
+			for mid < len(nums) {
+				if nums[mid+1] == value {
+					mid++
+				} else {
+					return mid
+				}
+			}
+		}
+	}
+	return -1
+}
+
+// 查找第一个大于等于给定值的元素
+func BinarySearch4(nums []int, value int) int {
+	start := 0
+	end := len(nums) - 1
+	for start <= end {
+		mid := (start + end) >> 1
+		if nums[mid] < value {
+			start = mid + 1
+		} else {
+			for mid >= 0 {
+				if nums[mid-1] >= value {
+					mid--
+				} else {
+					return mid
+				}
+			}
+		}
+	}
+	return -1
+}
+
+// 查找最后一个小于等于给定值的元素
+func BinarySearch5(nums []int, value int) int {
+	start := 0
+	end := len(nums) - 1
+	for start <= end {
+		mid := (start + end) >> 1
+		if nums[mid] > value {
+			end = mid - 1
+		} else {
+			for mid < len(nums) {
+				if nums[mid+1] <= value {
+					mid++
+				} else {
+					return mid
+				}
+			}
+		}
+	}
+	return -1
+}