MAY-25 2020 Challenge

Uncrossed Lines

We write the integers of A and B (in the order they are given) on two separate horizontal lines.
Now, we may draw connecting lines: a straight line connecting two numbers A[i] and B[j] such that:
A[i] == B[j];
The line we draw does not intersect any other connecting (non-horizontal) line.
Note that a connecting lines cannot intersect even at the endpoints: each number can only belong to one connecting line.
Return the maximum number of connecting lines we can draw in this way.

Example 1:

Input: A = [1,4,2], B = [1,2,4]
Output: 2
Explanation: We can draw 2 uncrossed lines as in the diagram.
We cannot draw 3 uncrossed lines, because the line from A[1]=4 to B[2]=4 will intersect the line from A[2]=2 to B[1]=2.

Example 2:

Input: A = [2,5,1,2,5], B = [10,5,2,1,5,2]
Output: 3

Example 3:

Input: A = [1,3,7,1,7,5], B = [1,9,2,5,1]
Output: 2

Note:

1 <= A.length <= 500

1 <= B.length <= 500

1 <= A[i], B[i] <= 2000

Solution in Python :

class Solution(object):

    def maxUncrossedLines(self, A, B):

        """

        :type A: List[int]

        :type B: List[int]

        :rtype: int

        """

        memo={}

        la,lb=len(A),len(B)

        def helper(i,j):

            if i>=la or j>=lb:

                return 0

            if (i,j) in memo:

                return memo[i,j]

            if A[i]==B[j]:

                ans=1+helper(i+1,j+1)

            else:

                ans=max(helper(i+1,j),helper(i,j+1))

            memo[i,j]=ans

            return ans

        return helper(0,0)