Add Substring Anagrams

Author: marttp

kotlin/Sliding Windows/SubstringAnagrams.kt

@@ -0,0 +1,35 @@
+fun substringAnagrams(s: String, t: String): Int {
+    val lenS = s.length
+    val lenT = t.length
+    if (lenT > lenS) {
+        return 0
+    }
+    var count = 0
+    val expectedFreqs = IntArray(26)
+    val windowFreqs = IntArray(26)
+    // Populate 'expected_freqs' with the characters in string 't'.
+    for (c in t) {
+        expectedFreqs[c - 'a']++
+    }
+    var left = 0
+    var right = 0
+    while (right < lenS) {
+        // Add the character at the right pointer to 'window_freqs'
+        // before sliding the window.
+        windowFreqs[s[right] - 'a']++
+        // If the window has reached the expected fixed length, we
+        // advance the left pointer as well as the right pointer to
+        // slide the window.
+        if (right - left + 1 == lenT) {
+            if (windowFreqs.contentEquals(expectedFreqs)) {
+                count++
+            }
+            // Remove the character at the left pointer from
+            // 'window_freqs' before advancing the left pointer.
+            windowFreqs[s[left] - 'a']--
+            left++
+        }
+        right++
+    }
+    return count
+}