Number of excellent pairs

Array Hash Table Binary Search Bit Manipulation

49.0% acceptance

Feb 25, 2026

619

You are given a 0-indexed positive integer array nums and a positive integer k. A pair of numbers (num1, num2) is called excellent if the following conditions are satisfied: Both the numbers num1 and num2 exist in the array nums. The sum of the number of set bits in num1 OR num2 and num1 AND num2 is greater than or equal to k, where OR is the bitwise OR operation and AND is the bitwise AND operation. Return the number of distinct excellent pairs. Two pairs (a, b) and (c, d) are considered distinct if either a != c or b != d. For example, (1, 2) and (2, 1) are distinct. Note that a pair (num1, num2) such that num1 == num2 can also be excellent if you have at least one occurrence of num1 in the array.

Solution

Rust

Time O(n log n)

Space O(1)

LeetCode

solution.rs

use std::collections::HashSet;


impl Solution {
  pub fn count_excellent_pairs(nums: Vec<i32>, k: i32) -> i64 {
    let distinct: HashSet<i32> = nums.into_iter().collect();
    let mut pc: Vec<i32> = distinct.iter().map(|&n| n.count_ones() as i32).collect();
    pc.sort_unstable();
    let n = pc.len();
    let mut ans = 0i64;
    for i in 0..n {
      let need = k - pc[i];
      let j = pc.partition_point(|&x| x < need);
      ans += (n - j) as i64;
    }
    ans
  }
}