solves #2697: lexographically smallest palindrome

Author: anishLearnsToCode

Diff for: README.md

@@ -822,3 +822,4 @@
 | 2660 | [Determine the Winner of a Bowling Game](https://leetcode.com/problems/determine-the-winner-of-a-bowling-game)                                                         |                                                                              [![Java](assets/java.png)](src/DetermineTheWinnerOfABowlingGame.java)                                                                               |                                                                                                                                   |
 | 2670 | [Find the Distinct Difference Array](https://leetcode.com/problems/find-the-distinct-difference-array)                                                                 |                                                                               [![Java](assets/java.png)](src/FindTheDistinctDifferenceArray.java)                                                                                |                                                                                                                                   |
 | 2678 | [Number of Senior Citizens](https://leetcode.com/problems/number-of-senior-citizens)                                                                                   |                                                                                   [![Java](assets/java.png)](src/NumberOfSeniorCitizens.java)                                                                                    |                                                                                                                                   |
+| 268  | [Number of Senior Citizens](https://leetcode.com/problems/number-of-senior-citizens)                                                                                   |                                                                                   [![Java](assets/java.png)](src/NumberOfSeniorCitizens.java)                                                                                    |                                                                                                                                   |

Diff for: src/LexicographicallySmallestPalindrome.java

@@ -0,0 +1,27 @@
+// https://leetcode.com/problems/lexicographically-smallest-palindrome
+// T: O(N)
+// S: O(N)
+
+public class LexicographicallySmallestPalindrome {
+    public String makeSmallestPalindrome(String s) {
+        final StringBuilder firstPart = new StringBuilder();
+        final StringBuilder lastPart = new StringBuilder();
+
+        for (int i = 0 ; i < s.length() / 2 ; i++) {
+            char first = s.charAt(i), last = s.charAt(s.length() - 1 - i);
+            if (first != last) {
+                char smaller = (char) Math.min(first, last);
+                firstPart.append(smaller);
+                lastPart.append(smaller);
+            } else {
+                firstPart.append(first);
+                lastPart.append(first);
+            }
+        }
+
+        if (s.length() % 2 == 0) {
+            return firstPart.append(lastPart.reverse()).toString();
+        }
+        return firstPart.append(s.charAt(s.length() / 2)).append(lastPart.reverse()).toString();
+    }
+}