【算法模板】二分查找

二分查找

logn复杂度

• binary_search：点查
• left_bound：左边界
• right_bound：右边界

代码语言：javascript复制

func binary_search(nums []int, target int) int {
	left, right := 0, len(nums)-1
	for left <= right {
		mid := left   (right-left)/2
		if nums[mid] < target {
			left = mid   1
		} else if nums[mid] > target {
			right = mid - 1
		} else if nums[mid] == target {
			return mid
		}
	}
	return -1
}

func left_bound(nums []int, target int) int {
	left, right := 0, len(nums)-1
	for left <= right {
		mid := left   (right-left)/2
		if nums[mid] < target {
			left = mid   1
		} else if nums[mid] > target {
			right = mid - 1
		} else if nums[mid] == target {
			right = mid - 1
		}
	}
	if left >= len(nums) || nums[left] != target {
		return -1
	}
	return left
}

func right_bound(nums []int, target int) int {
	left, right := 0, len(nums)-1
	for left <= right {
		mid := left   (right-left)/2
		if nums[mid] < target {
			left = mid   1
		} else if nums[mid] > target {
			right = mid - 1
		} else if nums[mid] == target {
			left = mid   1
		}
	}
	if right < 0 || nums[right] != target {
		return -1
	}
	return right
}

binary search

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