Update 0567-permutation-in-string.java

java/0567-permutation-in-string.java

@@ -1,20 +1,59 @@
-public class Solution {
+class Solution {
+
     public boolean checkInclusion(String s1, String s2) {
+
         int n = s1.length();
-        int[] freq = new int[26];
         int m = s2.length();
-        for (int i = 0; i < n; i++) {
-            freq[s1.charAt(i) - 'a']++;
-        }
-        int[] freq2 = new int[26];
-        for (int i = 0; i < m; i++) {
-            freq2[s2.charAt(i) - 'a']++;
-            if (i >= n) {
-                freq2[s2.charAt(i - n) - 'a']--;
-            }
-            if (Arrays.equals(freq, freq2))
+
+        if(n > m)
+            return false;
+
+        int[] f1 = new int[26];
+        int[] f2 = new int[26];
+
+        for(int i=0; i<n; i++)
+            f1[s1.charAt(i)-'a']++;
+
+        for(int i=0; i<n; i++) // we will iterate only till n chars since those will form the initial permutation
+            f2[s2.charAt(i)-'a']++;
+
+        if (Arrays.equals(f1, f2))
+            return true;
+
+        int idx = n; // start of next window
+
+        while(idx < m){
+
+            // we have moved the window one step towards right
+            // so freq of char at idx should increase
+            // and freq of left most char in prev window should decrease
+            char newChar = s2.charAt(idx);
+            char prevChar = s2.charAt(idx-n);
+
+            f2[newChar-'a']++;
+            f2[prevChar-'a']--;
+
+            if (Arrays.equals(f1, f2))
                 return true;
+
+            idx++;
+
         }
+
         return false;
+
+    }
+
+    public int initializeMatch(int[] f1, int[] f2){
+
+        int count = 0;
+
+        for(int i=0; i<26; i++){
+            if(f1[i] == f2[i])
+                count++;
+        }
+
+        return count;
     }
-}
+
+}