longest palindromic substring solution

Author: yhkee0404

longest-palindromic-substring/yhkee0404.scala

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+import scala.collection.mutable.ArrayBuffer
+
+object Solution {
+    def longestPalindrome(s: String): String = {
+        val list = ArrayBuffer[Char]()
+        for (c <- s) {
+            list += c
+            list += '\u0000'
+        }
+        val dp = Array.fill(list.size - 1)(0)
+        var lastR = -1
+        var lastMid = -1
+        var maxD = 0
+        var ansL = 0
+        var ansR = 0
+        var i = 1
+        for (i <- 0 until dp.size) { // Manacher T(n) = S(n) = O(n)
+            val diff = lastR - i
+            var d = if (diff <= 0) 0 else diff min dp((lastMid << 1) - i)
+            var l = i - d
+            var r = i + d
+            while (l != 0 && r != list.size - 1 && list(l - 1) == list(r + 1)) {
+                d += 1
+                l -= 1
+                r += 1
+            }
+            if (maxD < d) {
+                maxD = d
+                ansL = l
+                ansR = r
+            }
+            dp(i) = d
+            if (lastR < r) {
+                lastR = r
+                lastMid = i
+            }
+        }
+        val sb = StringBuilder()
+        for (i <- ansL to ansR if list(i) != '\u0000') {
+            sb.append(list(i))
+        }
+        sb.toString
+    }
+}