Question

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

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Description

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.

 

Constraints:

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

Solutions

Solution 1

class Solution:
  def specialArray(self, nums: List[int]) -> int:
    for x in range(1, len(nums) + 1):
      cnt = sum(v >= x for v in nums)
      if cnt == x:
        return x
    return -1

class Solution {
  public int specialArray(int[] nums) {
    for (int x = 1; x <= nums.length; ++x) {
      int cnt = 0;
      for (int v : nums) {
        if (v >= x) {
          ++cnt;
        }
      }
      if (cnt == x) {
        return x;
      }
    }
    return -1;
  }
}

class Solution {
public:
  int specialArray(vector<int>& nums) {
    for (int x = 1; x <= nums.size(); ++x) {
      int cnt = 0;
      for (int v : nums) cnt += v >= x;
      if (cnt == x) return x;
    }
    return -1;
  }
};

func specialArray(nums []int) int {
  for x := 1; x <= len(nums); x++ {
    cnt := 0
    for _, v := range nums {
      if v >= x {
        cnt++
      }
    }
    if cnt == x {
      return x
    }
  }
  return -1
}

function specialArray(nums: number[]): number {
  const n = nums.length;
  for (let i = 0; i <= n; i++) {
    if (i === nums.reduce((r, v) => r + (v >= i ? 1 : 0), 0)) {
      return i;
    }
  }
  return -1;
}

impl Solution {
  pub fn special_array(nums: Vec<i32>) -> i32 {
    let n = nums.len() as i32;
    for i in 0..=n {
      let mut count = 0;
      for &num in nums.iter() {
        if num >= i {
          count += 1;
        }
      }
      if count == i {
        return i;
      }
    }
    -1
  }
}

Solution 2

class Solution:
  def specialArray(self, nums: List[int]) -> int:
    nums.sort()
    n = len(nums)
    for x in range(1, n + 1):
      cnt = n - bisect_left(nums, x)
      if cnt == x:
        return x
    return -1

class Solution {
  public int specialArray(int[] nums) {
    Arrays.sort(nums);
    int n = nums.length;
    for (int x = 1; x <= n; ++x) {
      int left = 0, right = n;
      while (left < right) {
        int mid = (left + right) >> 1;
        if (nums[mid] >= x) {
          right = mid;
        } else {
          left = mid + 1;
        }
      }
      int cnt = n - left;
      if (cnt == x) {
        return x;
      }
    }
    return -1;
  }
}

class Solution {
public:
  int specialArray(vector<int>& nums) {
    int n = nums.size();
    sort(nums.begin(), nums.end());
    for (int x = 1; x <= n; ++x) {
      int cnt = n - (lower_bound(nums.begin(), nums.end(), x) - nums.begin());
      if (cnt == x) return x;
    }
    return -1;
  }
};

func specialArray(nums []int) int {
  sort.Ints(nums)
  n := len(nums)
  for x := 1; x <= n; x++ {
    left, right := 0, n
    for left < right {
      mid := (left + right) >> 1
      if nums[mid] >= x {
        right = mid
      } else {
        left = mid + 1
      }
    }
    cnt := n - left
    if cnt == x {
      return x
    }
  }
  return -1
}

function specialArray(nums: number[]): number {
  const n = nums.length;
  let left = 0;
  let right = n + 1;
  while (left < right) {
    const mid = (left + right) >> 1;
    const count = nums.reduce((r, v) => r + (v >= mid ? 1 : 0), 0);

    if (count === mid) {
      return mid;
    }

    if (count > mid) {
      left = mid + 1;
    } else {
      right = mid;
    }
  }
  return -1;
}

use std::cmp::Ordering;
impl Solution {
  pub fn special_array(nums: Vec<i32>) -> i32 {
    let n = nums.len() as i32;
    let mut left = 0;
    let mut right = n + 1;
    while left < right {
      let mid = left + (right - left) / 2;
      let mut count = 0;
      for &num in nums.iter() {
        if num >= mid {
          count += 1;
        }
      }
      match count.cmp(&mid) {
        Ordering::Equal => {
          return mid;
        }
        Ordering::Less => {
          right = mid;
        }
        Ordering::Greater => {
          left = mid + 1;
        }
      }
    }
    -1
  }
}