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
public class Solution {
public int SpecialArray(int[] nums) {
int x = nums.Length;
var counts = new int[x+1];
foreach(var elem in nums){
if(elem >= x){
counts[x]++;
}
else{
counts[elem]++;
}
}
int res = 0;
for(int i = counts.Length-1; i > 0; i--) {
res += counts[i];
if(res == i){
return i;
}
}
return -1;
}
}
Time Complexity: O(n)
Space Complexity: O(n)