class Solution(object):
    def getCount(self, d, nums, size):
        j,count = 0, 0
        for i in range(1, size):
            while nums[i]-nums[j] > d: j+=1
            count += i-j
        return count
    def smallestDistancePair(self, nums, k):
        nums.sort()
        size = len(nums) 
        l = 0
        r = nums[size-1] - nums[0]
        while l<r:
            mid = (l+r) >> 1
            count = self.getCount(mid, nums, size)
            if count < k: l = mid+1
            else: r = mid
        return r