Special array with x elements greater than or equal x

Array Binary Search Sorting

66.8% acceptance

Feb 25, 2026

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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.

Solution

Rust

Time O(n log n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn special_array(mut nums: Vec<i32>) -> i32 {
    nums.sort();
    let n = nums.len() as i32;
    for x in 0..=n {
      // count elements >= x
      let cnt = nums.partition_point(|&v| v < x) as i32;
      let ge = n - cnt;
      if ge == x {
        return x;
      }
    }
    -1
  }
}