Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 14

Description

Find K-th Smallest Pair Distance

The distance of a pair of integers a and b is defined as the absolute difference between a and b.

Given an integer array nums and an integer k, return the kth smallest distance among all the pairs nums[i] and nums[j] where 0 <= i < j < nums.length.

Example 1:

Input: nums = [1,3,1], k = 1
Output: 0
Explanation: Here are all the pairs:
(1,3) -> 2
(1,1) -> 0
(3,1) -> 2
Then the 1st smallest distance pair is (1,1), and its distance is 0.

Example 2:

Input: nums = [1,1,1], k = 2
Output: 0

Example 3:

Input: nums = [1,6,1], k = 3
Output: 5

Constraints:

• n == nums.length
• 2 <= n <= 104
• 0 <= nums[i] <= 106
• 1 <= k <= n * (n - 1) / 2

Solution

class Solution {
  int countPairs(int x, vector<int> &nums) {
    int len = nums.size();
    int count = 0;
    for(int l = 0, r = 1; r < len; ++r) {
      while(r > l && nums[r] - nums[l] > x) {
        l += 1;
      }
      count += r - l;
    }
    return count;

  }
public:
  int smallestDistancePair(vector<int>& nums, int k) {
    sort(nums.begin(), nums.end());
    int high = nums.back();
    int low = 0;
    while(low < high) {
      int mid = (low + high) / 2;
      if(countPairs(mid, nums) < k) {
        low = mid + 1;
      } else {
        high = mid;
      }
    }
    return low;
  }
};