LeetCode [1608] Special Array With X Elements Greater Than or Equal X

 1608. Special Array With X Elements Greater Than or Equal X

Easy

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: 2
Explanation: There are 2 values (3 and 5) that are greater than or equal to 2.

Example 2:

Input: nums = [0,0]
Output: -1
Explanation: 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: 3
Explanation: There are 3 values that are greater than or equal to 3.

Example 4:

Input: nums = [3,6,7,7,0]
Output: -1

 

Constraints:

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

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class Solution { public int specialArray(int[] nums) { int n = nums.length, l = 0, r = n-1; Arrays.sort(nums); while(l<=r){ int m = (l+r)/2; // System.out.println(l+" "+m+" "+r); int x = n-m; if(nums[m]>=x && (m==0 || nums[m-1]<x)) return x; if(nums[m]<x){ l = m+1; }else{ r = m-1; } } return -1; } }