ImmutableStringRollingHash実装

src/main/kotlin/string/ImmutableStringRollingHash.kt

@@ -1,11 +1,16 @@
 package string
 
-class ImmutableStringRollingHash(private val radix: Long) {
+import kotlin.random.Random
+
+class ImmutableStringRollingHash {
     companion object {
         private const val MOD = (1L shl 61) - 1
         private const val MASK31 = (1L shl 31) - 1
         private const val MASK30 = (1L shl 30) - 1
 
+        // 文字列最大長、適宜変更すること
+        private const val MAX_LENGTH = 5000000
+
         private fun multiply(l: Long, r: Long): Long {
             val au = l shr 31
             val ad = l and MASK31
@@ -24,4 +29,24 @@ class ImmutableStringRollingHash(private val radix: Long) {
             return ((num % MOD) + MOD) % MOD
         }
     }
+
+    private val radix = Random.nextLong(MOD)
+    private val p = LongArray(MAX_LENGTH + 1) { 1 }
+
+    init {
+        for (i in 0 until MAX_LENGTH) {
+            p[i + 1] = multiply(p[i], radix)
+        }
+    }
+
+    fun createGetHash(s: String) = createGetHash(s.toCharArray())
+
+    fun createGetHash(array: CharArray): (Int, Int) -> Pair<Long, Int> {
+        val len = array.size
+        val table = LongArray(len + 1) { 0 }
+        for (i in array.indices) {
+            table[i + 1] = safeMod(multiply(radix, table[i]) + array[i].code)
+        }
+        return { begin, end -> safeMod(table[end] - multiply(p[end - begin], table[begin])) to end - begin }
+    }
 }