problems: add „30. Substring with Concatenation of All Words“

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/substring-with-concatenation-of-all-words.kt

@@ -0,0 +1,29 @@
+class Solution {
+    private fun buildTable(words: Sequence<String>): Map<String, Int> {
+        val table = mutableMapOf<String, Int>()
+
+        words.forEach {
+            table.put(it, 1 + table.getOrElse(it) { 0 })
+        }
+
+        return table
+    }
+    private fun buildTable(s: String, length: Int): Map<String, Int> =
+        buildTable(s.chunked(length).asSequence())
+
+    fun findSubstring(s: String, words: Array<String>): List<Int> {
+        val expectedFrequencies = buildTable(words.asSequence())
+        val wordLen = words.first().length
+        val windowSize = wordLen * words.size
+
+        return s
+            .windowed(windowSize)
+            .zip(s.indices)
+            .filter { (window, _) ->
+                val frequencies = buildTable(window, wordLen)
+                frequencies == expectedFrequencies
+            }
+            .map { (_, idx) -> idx }
+            .toList()
+    }
+}