Soyo

May Leetcode Challenge - Day 25

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

It's similar to LongestCommongSubsequence
dp[i][j] = max(dp[i-1][j], dp[i][j-1])

class Solution {
    func maxUncrossedLines(_ A: [Int], _ B: [Int]) -> Int {
        var dp = Array(repeating: Array(repeating: 0, count: B.count + 1), count: A.count + 1)
        
        for i in 1...A.count {
            for j in 1...B.count {
                if A[i-1] == B[j-1] {
                    dp[i][j] = 1 + dp[i-1][j-1]
                }else{
                    dp[i][j] = max(dp[i-1][j], dp[i][j-1])
                }
            }
        }
        
        return dp[A.count][B.count]
    }
}

Comments