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Formatted question description: https://leetcode.ca/all/2354.html

2354. Number of Excellent Pairs

  • Difficulty: Hard.
  • Related Topics: Array, Hash Table, Binary Search, Bit Manipulation.
  • Similar Questions: Two Sum.

Problem

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.

  Example 1:

Input: nums = [1,2,3,1], k = 3
Output: 5
Explanation: The excellent pairs are the following:
- (3, 3). (3 AND 3) and (3 OR 3) are both equal to (11) in binary. The total number of set bits is 2 + 2 = 4, which is greater than or equal to k = 3.
- (2, 3) and (3, 2). (2 AND 3) is equal to (10) in binary, and (2 OR 3) is equal to (11) in binary. The total number of set bits is 1 + 2 = 3.
- (1, 3) and (3, 1). (1 AND 3) is equal to (01) in binary, and (1 OR 3) is equal to (11) in binary. The total number of set bits is 1 + 2 = 3.
So the number of excellent pairs is 5.

Example 2:

Input: nums = [5,1,1], k = 10
Output: 0
Explanation: There are no excellent pairs for this array.

  Constraints:

  • 1 <= nums.length <= 105

  • 1 <= nums[i] <= 109

  • 1 <= k <= 60

Solution

  • class Solution {
    public long countExcellentPairs(int[] nums, int k) {
        long[] cnt = new long[30];
        long res = 0L;
        Set<Integer> set = new HashSet<>();
        for (int a : nums) {
            set.add(a);
        }
        for (int a : set) {
            cnt[Integer.bitCount(a)]++;
        }
        for (int i = 1; i < 30; ++i) {
            for (int j = 1; j < 30; ++j) {
                if (i + j >= k) {
                    res += cnt[i] * cnt[j];
                }
            }
        }
        return res;
    }
}

############

class Solution {
    public long countExcellentPairs(int[] nums, int k) {
        Set<Integer> s = new HashSet<>();
        for (int v : nums) {
            s.add(v);
        }
        long ans = 0;
        int[] cnt = new int[32];
        for (int v : s) {
            int t = Integer.bitCount(v);
            ++cnt[t];
        }
        for (int v : s) {
            int t = Integer.bitCount(v);
            for (int i = 0; i < 32; ++i) {
                if (t + i >= k) {
                    ans += cnt[i];
                }
            }
        }
        return ans;
    }
}

  • class Solution:
    def countExcellentPairs(self, nums: List[int], k: int) -> int:
        s = set(nums)
        ans = 0
        cnt = Counter()
        for v in s:
            cnt[v.bit_count()] += 1
        for v in s:
            t = v.bit_count()
            for i, x in cnt.items():
                if t + i >= k:
                    ans += x
        return ans

############

# 2354. Number of Excellent Pairs
# https://leetcode.com/problems/number-of-excellent-pairs/

class Solution:
    def countExcellentPairs(self, nums: List[int], k: int) -> int:
        nums = set(nums)
        
        MAX = 32
        bits = [0] * MAX
        
        for x in nums:
            bits[x.bit_count()] += 1
        
        res = 0
        for i in range(1, MAX):
            for j in range(1, MAX):
                if i + j >= k:
                    res += bits[i] * bits[j]
        
        return res
        


  • class Solution {
public:
    long long countExcellentPairs(vector<int>& nums, int k) {
        unordered_set<int> s(nums.begin(), nums.end());
        vector<int> cnt(32);
        for (int v : s) ++cnt[__builtin_popcount(v)];
        long long ans = 0;
        for (int v : s) {
            int t = __builtin_popcount(v);
            for (int i = 0; i < 32; ++i) {
                if (t + i >= k) {
                    ans += cnt[i];
                }
            }
        }
        return ans;
    }
};

  • func countExcellentPairs(nums []int, k int) int64 {
	s := map[int]bool{}
	for _, v := range nums {
		s[v] = true
	}
	cnt := make([]int, 32)
	for v := range s {
		t := bits.OnesCount(uint(v))
		cnt[t]++
	}
	ans := 0
	for v := range s {
		t := bits.OnesCount(uint(v))
		for i, x := range cnt {
			if t+i >= k {
				ans += x
			}
		}
	}
	return int64(ans)
}

Explain:

nope.

Complexity:

  • Time complexity : O(n).
  • Space complexity : O(n).

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