add a solution for 567

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_567.java

@@ -43,4 +43,46 @@ private boolean allZeroes(int[] count) {
             return true;
         }
     }
+
+    public static class Solution2 {
+        /**
+         * A classic sliding window problem.
+         * I came up with below solution independently on 9/17/2021.
+         * <p>
+         * A few pointers that led me to the sliding window approach:
+         * 1. if it's a valid permutation, the substring from S2 must have equal length as of s1;
+         * 2. I don't want to repeatedly calculate each and every possible substring of s2, if s1 is really long, this could mean lots of redundant calculation.
+         * So sliding window to the rescue!
+         */
+        public boolean checkInclusion(String s1, String s2) {
+            if (s1.length() > s2.length()) {
+                return false;
+            }
+            int[] count = new int[26];
+            for (char c : s1.toCharArray()) {
+                count[c - 'a']++;
+            }
+            for (int i = 0; i < s1.length(); i++) {
+                count[s2.charAt(i) - 'a']--;
+            }
+            for (int i = s1.length(), j = 0; i < s2.length(); i++, j++) {
+                if (isPermutation(count)) {
+                    return true;
+                } else {
+                    count[s2.charAt(j) - 'a']++;
+                    count[s2.charAt(i) - 'a']--;
+                }
+            }
+            return isPermutation(count);
+        }
+
+        private boolean isPermutation(int[] count) {
+            for (int c : count) {
+                if (c != 0) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
 }

src/test/java/com/fishercoder/_567Test.java

@@ -8,6 +8,7 @@
 
 public class _567Test {
     private static _567.Solution1 solution1;
+    private static _567.Solution2 solution2;
     private static boolean expected;
     private static boolean actual;
     private static String s1;
@@ -16,6 +17,7 @@ public class _567Test {
     @BeforeClass
     public static void setup() {
         solution1 = new _567.Solution1();
+        solution2 = new _567.Solution2();
     }
 
     @Test
@@ -24,6 +26,17 @@ public void test1() {
         s2 = "eidbaooo";
         expected = true;
         actual = solution1.checkInclusion(s1, s2);
+        actual = solution2.checkInclusion(s1, s2);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test2() {
+        s1 = "adc";
+        s2 = "dcda";
+        expected = true;
+        actual = solution1.checkInclusion(s1, s2);
+        actual = solution2.checkInclusion(s1, s2);
         assertEquals(expected, actual);
     }
 }