You are given two sorted lists of size m and n. Implement a function to find the kth smallest element in the union of the two lists with linear complexity.

To find the k th smallest element in the union of two sorted lists with linear complexity , we can use the following approach : \n \n 1 . Sort both lists and store them in two arrays ` a ` and ` b `. \n 2 . Initialize two pointers ` i ` and ` j ` to point to the beginning of the two arrays . \n 3 . Initialize a counter ` k ` to store the position of the k th smallest element . \n 4 . While ` i ` is less than ` j ` and ` k ` is less than ` k `, do the following : \n 1 . If ` a [ i ] <= b [ j ] `, update ` k ` with ` k + 1 `. \n 2 . If ` a [ i ] b [ j ] `, update ` i ` with ` i + 1 `. \n 3 . If ` a [ i ] <</a> b [ j ] `, update ` j ` with ` j - 1 `. \n 5 . The element at position ` k ` in the union of the two lists is the k th smallest element . \n \n The time complexity of this algorithm is O ( m + n ) due to the two sorting operations and the two pointer movements . The space complexity is O ( 1 ) as we are only using two arrays of size m and n , respectively . </s>