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by AskGif | Oct 18, 2020 | Category :coding | Tags : algorithm array data-structure easy leetcode

Special Array With X Elements Greater Than or Equal X - Array - Easy - LeetCode

Special Array With X Elements Greater Than or Equal X - Array - Easy - LeetCode

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)