動機

猜數字

Problem

You are given an array nums of non-negative integers. nums is considered special if there exists a number x such that there are exactly x numbers in nums that are greater than or equal to x.

Notice that x does not have to be an element in nums.

Return x if the array is special, otherwise, return -1. It can be proven that if nums is special, the value for x is unique.

 

Example 1:

Input: nums = [3,5]Output: 2Explanation: There are 2 values (3 and 5) that are greater than or equal to 2.

Example 2:

Input: nums = [0,0]Output: -1Explanation: No numbers fit the criteria for x.If x = 0, there should be 0 numbers >= x, but there are 2.If x = 1, there should be 1 number >= x, but there are 0.If x = 2, there should be 2 numbers >= x, but there are 0.x cannot be greater since there are only 2 numbers in nums.

Example 3:

Input: nums = [0,4,3,0,4]Output: 3Explanation: There are 3 values that are greater than or equal to 3.

 

Constraints:

  • 1 <= nums.length <= 100
  • 0 <= nums[i] <= 1000

sol

class Solution:
    def specialArray(self, nums: List[int]) -> int:
        a,b = 0, len(nums)
        nums.sort()
        while a<b:
            mid = (a+b)//2
            tmp = len(nums)-bisect_left(nums, mid)
            if len(nums)-bisect_left(nums, mid) > mid:
                a = mid+1
            else:
                b = mid
        return a if len(nums)-bisect_left(nums, a) == a else -1