题目：

题解：

class Solution:
    def kSmallestPairs(self, nums1: List[int], nums2: List[int], k: int) -> List[List[int]]:
        m, n = len(nums1), len(nums2)

        # 二分查找第 k 小的数对和
        left, right = nums1[0] + nums2[0], nums1[m - 1] + nums2[n - 1] + 1
        while left < right:
            mid = (left + right) // 2
            cnt = 0
            i, j = 0, n - 1
            while i < m and j >= 0:
                if nums1[i] + nums2[j] > mid:
                    j -= 1
                else:
                    cnt += j + 1
                    i += 1
            if cnt < k:
                left = mid + 1
            else:
                right = mid
        pairSum = left

        ans = []
        # 找数对和小于 pairSum 的数对
        i = n - 1
        for num1 in nums1:
            while i >= 0 and num1 + nums2[i] >= pairSum:
                i -= 1
            for j in range(i + 1):
                ans.append([num1, nums2[j]])
                if len(ans) == k:
                    return ans

        # 找数对和等于 pairSum 的数对
        i = n - 1
        for num1 in nums1:
            while i >= 0 and num1 + nums2[i] > pairSum:
                i -= 1
            j = i
            while j >= 0 and num1 + nums2[j] == pairSum:
                ans.append([num1, nums2[j]])
                if len(ans) == k:
                    return ans
                j -= 1
        return ans