Program to find k where k elements have value at least k in Python

Suppose we have a list of numbers called nums, that contains only non-negative numbers. If there are exactly k number of elements in nums that are greater than or equal to k, find the value k. If we cannot find such, then return -1.

So, if the input is like nums = [6, 4, 0, 8, 2, 9], then the output will be 4, because there are exactly 4 elements that are greater than or equal to 4: [6, 4, 8, 9].

To solve this, we will follow these steps −

• sort the list nums in reverse order

• for i in range 1 to size of nums - 1, do

  • if i > nums[i - 1], then

    • come out from loop

  • otherwise when i > nums[i], then

    • return i

• return -1

Example

Let us see the following implementation to get better understanding

def solve(nums):
   nums.sort(reverse=True)
   for i in range(1, len(nums)):
      if i >nums[i - 1]:
         break
      elif i > nums[i]:
         return i
   return -1

nums = [6, 4, 0, 8, 2, 9]
print(solve(nums))

Input

[6, 4, 0, 8, 2, 9]

Output

4