HàPhan 河

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=4 to B=4 will intersect the line from A=2 to B=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]
}
}
``````