Create 0451-sort-characters-by-frequency.kt

Author: a93a

kotlin/0451-sort-characters-by-frequency.kt

@@ -0,0 +1,47 @@
+// Count and bucketsort by freq
+class Solution {
+    fun frequencySort(s: String): String {
+        val counts = s
+            .groupingBy { it }
+            .eachCount()
+
+        val buckets = HashMap<Int, MutableList<Char>>()
+        for ((char, count) in counts)
+            buckets.getOrPut(count) { mutableListOf() }.apply { add(char) }
+
+        val res = StringBuilder()
+        for (count in s.length downTo 1) {
+            buckets[count]?.forEach { char ->
+                repeat (count) {
+                    res.append(char)
+                }
+            }
+        }
+
+        return res.toString()
+    }
+}
+
+// Count and sort
+class Solution {
+    fun frequencySort(s: String): String {
+        val counts = IntArray (128)
+        
+        for (c in s)
+            counts[c.toInt()]++
+
+        val sortedCounts = counts
+            .mapIndexed { i, v -> i to v }
+            .filter { it.second > 0 }
+            .sortedWith(compareBy({ -it.second },{ it.first }))
+
+        val res = StringBuilder ()
+        for ((char, count) in sortedCounts) {
+            repeat (count) {
+                res.append(char.toChar())
+            }
+        }
+
+        return res.toString()
+    }
+}