refactor 1576

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_1576.java

@@ -2,35 +2,27 @@
 
 public class _1576 {
     public static class Solution1 {
+        /**
+         * Each char could have at most two neighbors, so we only need to toggle between three character candidates to avoid repetition.
+         */
         public String modifyString(String s) {
-            StringBuilder sb = new StringBuilder();
-            for (int i = 0; i < s.length(); i++) {
-                char c = s.charAt(i);
-                if (c == '?') {
-                    char replacement = findReplacement(sb, i, s);
-                    sb.append(replacement);
-                } else {
-                    sb.append(c);
+            char[] arr = s.toCharArray();
+            for (int i = 0; i < arr.length; i++) {
+                if (arr[i] == '?') {
+                    for (int j = 0; j < 3; j++) {
+                        if (i > 0 && arr[i - 1] == 'a' + j) {
+                            continue;
+                        } else if (i < arr.length - 1 && arr[i + 1] == 'a' + j) {
+                            continue;
+                        } else {
+                            arr[i] = (char) ('a' + j);
+                            break;
+                        }
+                    }
                 }
             }
-            return sb.toString();
+            return String.valueOf(arr);
         }
 
-        private char findReplacement(StringBuilder sb, int index, String s) {
-            char replacement = 'a';
-            if (index > 0) {
-                int count = 1;
-                while (replacement == sb.charAt(index - 1)) {
-                    replacement += count % 26;
-                }
-            }
-            if (index + 1 < s.length()) {
-                int count = 1;
-                while (replacement == s.charAt(index + 1) || (index > 0 && replacement == sb.charAt(index - 1))) {
-                    replacement += count % 26;
-                }
-            }
-            return replacement;
-        }
     }
 }