minimum window substring solution

Author: yhkee0404

minimum-window-substring/yhkee0404.kt

@@ -0,0 +1,33 @@
+class Solution {
+    fun minWindow(s: String, t: String): String { // T(m, n) = S(m, n) = O(m + n)
+        val counterT = (
+            t
+            .groupingBy {it} // O(n)
+            .eachCount()
+        )
+        var l = -1
+        var r = -1
+        val counterS = mutableMapOf<Char, Int>()
+        var i = -1
+        (
+            s
+            .withIndex()
+            .forEach { // O(m)
+                counterS.compute(it.value) {k, v -> if (v == null) 1 else v + 1}
+                while (i != it.index && counterS[s[i + 1]]!! > counterT.getOrDefault(s[i + 1], 0)) { // O(m)
+                    counterS.compute(s[++i]) {k, v -> v!! - 1}
+                }
+                if (
+                    counterT
+                    .all {(k, v) -> counterS.getOrDefault(k, 0) >= v} // O(n)
+                ) {
+                    if (r == -1 || r - l > it.index - i) {
+                        l = i
+                        r = it.index
+                    }
+                }
+            }
+        )
+        return s.substring(l + 1, r + 1) // O(m)
+    }
+}