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Median of Two Sorted Arrays

Problem Statement​

Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.

The overall run time complexity should be O(log (m+n)).

Leetcode Link

Example 1:​

Input: nums1 = [1,3], nums2 = [2]
Output: 2.00000
Explanation: merged array = [1,2,3] and median is 2.

Example 2:​

Input: nums1 = [1,2], nums2 = [3,4]
Output: 2.50000
Explanation: merged array = [1,2,3,4] and median is (2 + 3) / 2 = 2.5.

Constraints:​

  • nums1.length == m
  • nums2.length == n
  • 0 <= m <= 1000
  • 0 <= n <= 1000
  • 1 <= m + n <= 2000
  • -106 <= nums1[i], nums2[i] <= 106

Code​

Python Code

class Solution:
    def findMedianSortedArrays(self, A, B):
        l = len(A) + len(B)
        if l % 2 == 1:
            return self.kth(A, B, l // 2)
        else:
            return (self.kth(A, B, l // 2) + self.kth(A, B, l // 2 - 1)) / 2.

    def kth(self, a, b, k):
        if not a:
            return b[k]
        if not b:
            return a[k]
        ia, ib = len(a) // 2 , len(b) // 2
        ma, mb = a[ia], b[ib]

        # when k is bigger than the sum of a and b's median indices
        if ia + ib < k:
            # if a's median is bigger than b's, b's first half doesn't include k
            if ma > mb:
                return self.kth(a, b[ib + 1:], k - ib - 1)
            else:
                return self.kth(a[ia + 1:], b, k - ia - 1)
        # when k is smaller than the sum of a and b's indices
        else:
            # if a's median is bigger than b's, a's second half doesn't include k
            if ma > mb:
                return self.kth(a[:ia], b, k)
            else:
                return self.kth(a, b[:ib], k)