Anagrams in string: done

Author: rampatra

README.md

@@ -32,7 +32,8 @@ You can also refer to my [Java Notes](http://java.ramswaroop.me) for a quick ref
     4. [Trees and Graphs](/src/main/java/com/ctci/treesandgraphs)
     5. [Bit Manipulation](/src/main/java/com/ctci/bitmanipulation)
     6. [Recursion and DP](/src/main/java/com/ctci/recursionanddp)
-3. [HackerRank](/src/main/java/com/hackerrank).
+3. [LeetCode](/src/main/java/com/leetcode).
+4. [HackerRank](/src/main/java/com/hackerrank).
 
 
 ## Environment

src/main/java/com/leetcode/strings/AnagramsInString.java

@@ -6,47 +6,102 @@
 
 /**
  * Leetcode Problem: https://leetcode.com/problems/find-all-anagrams-in-a-string/
- * 
+ *
  * @author rampatra
  * @since 2019-04-13
  */
 public class AnagramsInString {
 
+    /**
+     * Time complexity: O ((n-m) * m log m)
+     * where,
+     * n = text length
+     * m = pattern length
+     *
+     * @param text
+     * @param pattern
+     * @return
+     */
     private static List<Integer> findAllAnagramsInTextNaive(String text, String pattern) {
         List<Integer> indexes = new ArrayList<>();
-        
+
         int textLen = text.length();
         int patternLen = pattern.length();
-        
+
         char[] patternChars = pattern.toCharArray();
         Arrays.sort(patternChars); // takes O(m log m) time
         String patternSorted = String.valueOf(patternChars);
-        
+
         String subText;
         char[] subTextChars;
         String subTextSorted;
-        
+
         for (int i = 0; i <= textLen - patternLen; i++) { // loops n-m number of times
-            subText = text.substring(i, i + patternLen); 
+            subText = text.substring(i, i + patternLen);
             subTextChars = subText.toCharArray();
             Arrays.sort(subTextChars); // sorts m number of characters, takes O(m log m)
             subTextSorted = String.valueOf(subTextChars);
-            
+
             if (subTextSorted.equals(patternSorted)) { // compare m characters takes m time
                 indexes.add(i);
             }
         }
         return indexes;
     }
-    
+
+    /**
+     * Time complexity: O(n). Completes within <a href="https://leetcode.com/submissions/detail/222911434/">7ms on
+     * leetcode.</a>
+     *
+     * @param text
+     * @param pattern
+     * @return
+     */
+    private static List<Integer> findAllAnagramsInText(String text, String pattern) {
+        List<Integer> indices = new ArrayList<>();
+
+        int textLen = text.length();
+        int patternLen = pattern.length();
+
+        int[] textCharCountInWindow = new int[26];
+        int[] patternCharCount = new int[26];
+
+        for (int i = 0; i < patternLen; i++) {
+            patternCharCount[pattern.charAt(i) - 'a']++;
+        }
+
+        for (int i = 0; i < textLen; i++) {
+            textCharCountInWindow[text.charAt(i) - 'a']++;
+            if (i >= patternLen) {
+                textCharCountInWindow[text.charAt(i - patternLen) - 'a']--;
+            }
+            if (Arrays.equals(textCharCountInWindow, patternCharCount)) { // loops 26 times no matter the text/pattern length
+                indices.add(i - patternLen + 1);
+            }
+        }
+
+        return indices;
+    }
+
     public static void main(String[] args) {
         // basic use cases
         System.out.println(findAllAnagramsInTextNaive("cbaebabacd", "abc"));
         System.out.println(findAllAnagramsInTextNaive("abab", "ab"));
-        
-        // corner cases
-        System.out.println(findAllAnagramsInTextNaive("abab", ""));
+        System.out.println(findAllAnagramsInTextNaive("af", "af"));
+        System.out.println(findAllAnagramsInTextNaive("af", "be"));
+
+        // corner case
         System.out.println(findAllAnagramsInTextNaive("", "ab"));
-        System.out.println(findAllAnagramsInTextNaive("", ""));
+
+        System.out.println("-----");
+
+        // basic use cases
+        System.out.println(findAllAnagramsInText("cbaebabacd", "abc"));
+        System.out.println(findAllAnagramsInText("abab", "ab"));
+        System.out.println(findAllAnagramsInText("af", "af"));
+        System.out.println(findAllAnagramsInText("af", "be"));
+
+        // corner case
+        System.out.println(findAllAnagramsInText("", "ab"));
     }
 }