diff --git a/kt/minimum-window-substring.kt b/kt/minimum-window-substring.kt
new file mode 100644
index 0000000..4a3b184
--- /dev/null
+++ b/kt/minimum-window-substring.kt
@@ -0,0 +1,35 @@
+class Solution {
+    fun minWindow(s: String, t: String): String {
+        val freqs = IntArray(128) { 0 }
+        t.forEach {
+            freqs[it.toInt()]++
+        }
+
+        var (bestLower, bestUpper) = 0 to -1
+        var count = t.length
+        var (l, r) = 0 to 0
+
+        while (r < s.length) {
+            if (freqs[s[r].toInt()]-- > 0) {
+                count--
+            }
+
+            while (count == 0) {
+                if (bestLower >= bestUpper || bestUpper - bestLower + 1 > r - l + 1) {
+                    bestLower = l
+                    bestUpper = r
+                }
+
+                freqs[s[l].toInt()]++
+
+                if (freqs[s[l++].toInt()] > 0) {
+                    count++
+                }
+            }
+
+            r++
+        }
+
+        return s.substring(bestLower, bestUpper + 1)
+    }
+}