Create 0516-longest-palindromic-subsequence.swift

Author: drxlx

swift/0516-longest-palindromic-subsequence.swift

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+/**
+ * Question Link: https://leetcode.com/problems/longest-palindromic-subsequence/
+ */
+
+ class Solution {
+    func longestPalindromeSubseq(_ s: String) -> Int {
+        let s = Array(s)
+        let n = s.count
+        var dp = Array(repeating: 0, count: n)
+        var dpPrev = Array(repeating: 0, count: n)
+
+        for i in stride(from: s.count - 1, to: -1, by: -1) {
+            dp[i] = 1
+            for j in i + 1..<n {
+                if s[i] == s[j] {
+                    dp[j] = dpPrev[j - 1] + 2
+                } else {
+                    dp[j] = max(dpPrev[j], dp[j - 1])
+                }
+            }
+            dpPrev = dp
+        }
+
+        return dp[n - 1]
+    }
+}