二分模板

func binary_search(nums []int,target int) int {
    left,right := 0,len(nums) - 1
    for left <= right {
        mid := (left + right) >> 1
        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) >> 1
        if nums[mid] < target {
            left = mid + 1
        }else if nums[mid] > target{
            right = mid - 1;
        }else if nums[mid] == target{
            //别返回，锁定左侧边界
            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) >> 1
        if nums[mid] < target {
            left = mid + 1
        }else if nums[mid] > target{
            right = mid - 1;
        }else if nums[mid] == target{
            //别返回，锁定右侧边界
            left = mid + 1
        }
    }
    if right < 0 || nums[right] != target{
        return -1
    }
    return right
}