LeetCode in Erlang

4. Median of Two Sorted Arrays

Hard

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)).

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.

Example 3:

Input: nums1 = [0,0], nums2 = [0,0]

Output: 0.00000

Example 4:

Input: nums1 = [], nums2 = [1]

Output: 1.00000

Example 5:

Input: nums1 = [2], nums2 = []

Output: 2.00000

Constraints:

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

Solution

-spec find_median_sorted_arrays(Nums1 :: [integer()], Nums2 :: [integer()]) -> float().
find_median_sorted_arrays(Nums1, Nums2) -> 
    Len = length(Nums1) + length(Nums2),
    find_median_sorted_arrays(Nums1, Nums2, [], -1, 0, 0, Len rem 2, Len div 2).
find_median_sorted_arrays(_, _, [H|T], Index, _, _, Even, Index) ->
        if Even =:= 1 -> H;
            true -> (H + lists:nth(1, T)) / 2
        end;
find_median_sorted_arrays([], [H2|T2], MyArr, Index, Indx1, Indx2, Even, Middle) ->
    find_median_sorted_arrays([], T2, [H2|MyArr], Index + 1, Indx1, Indx2 + 1, Even, Middle);
find_median_sorted_arrays([H1|T1], [], MyArr, Index, Indx1, Indx2, Even, Middle) ->
    find_median_sorted_arrays(T1, [], [H1|MyArr], Index + 1, Indx1, Indx2 + 1, Even, Middle);
find_median_sorted_arrays([H1|T1], [H2|T2], MyArr, Index, Indx1, Indx2, Even, Middle) when H1 < H2 -> 
    find_median_sorted_arrays(T1, [H2|T2], [H1|MyArr], Index + 1, Indx1 + 1, Indx2, Even, Middle);
find_median_sorted_arrays([H1|T1], [H2|T2], MyArr, Index, Indx1, Indx2, Even, Middle)-> 
    find_median_sorted_arrays([H1|T1], T2, [H2|MyArr], Index + 1, Indx1, Indx2 + 1, Even, Middle).

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