solves longest nice substring

Author: anishLearnsToCode

README.md

@@ -430,7 +430,7 @@
 | 1748 | [Sum of Unique Elements](https://leetcode.com/problems/sum-of-unique-elements)                                                                            |                                                               [![Java](assets/java.png)](src/SumOfUniqueElements.java)                                                               |                                                                                                                                   |
 | 1752 | [Check if Array Is Sorted and Rotated](https://leetcode.com/problems/check-if-array-is-sorted-and-rotated)                                                |                                                         [![Java](assets/java.png)](src/CheckIfArrayIsSortedAndRotated.java)                                                          |                                                                                                                                   |
 | 1758 | [Minimum Changes To Make Alternating Binary String](https://leetcode.com/problems/minimum-changes-to-make-alternating-binary-string)                      |                                                   [![Java](assets/java.png)](src/MinimumChangesToMakeAlternatingBinaryString.java)                                                   |                                                                                                                                   |
-| 1763 | [Longest Nice Substring](https://leetcode.com/problems/longest-nice-substring)                                                                            |                                                                                                                                                                                      |                                                                                                                                   |
+| 1763 | [Longest Nice Substring](https://leetcode.com/problems/longest-nice-substring)                                                                            |                                                              [![Java](assets/java.png)](src/LongestNiceSubstring.java)                                                               |                                                                                                                                   |
 | 1768 | [Merge Strings Alternately](https://leetcode.com/problems/merge-strings-alternately)                                                                      |                                                                                                                                                                                      |                                                                                                                                   |
 | 1773 | [Count Items Matching a Rule](https://leetcode.com/problems/count-items-matching-a-rule)                                                                  |                                                                                                                                                                                      |                                                                                                                                   |
 | 1779 | [Find Nearest Point That Has the Same X or Y Coordinate](https://leetcode.com/problems/find-nearest-point-that-has-the-same-x-or-y-coordinate)            |                                                                                                                                                                                      |                                                                                                                                   |

src/LongestNiceSubstring.java

@@ -0,0 +1,40 @@
+import java.util.HashSet;
+import java.util.Set;
+
+public class LongestNiceSubstring {
+    public String longestNiceSubstring(String s) {
+        String longestNiceSubString = "";
+        Set<Character> alphabets = new HashSet<>();
+        for (int i = 0 ; i < s.length() ; i++) {
+            for (int j = i ; j < s.length() ; j++) {
+                alphabets.add(s.charAt(j));
+                if (containsBotLowerAndUpperCase(alphabets) && j - i + 1 > longestNiceSubString.length()) {
+                    longestNiceSubString = s.substring(i, j + 1);
+                }
+            }
+            alphabets.clear();
+        }
+        return longestNiceSubString;
+    }
+
+    private boolean containsBotLowerAndUpperCase(Set<Character> alphabets) {
+        for (char alphabet : alphabets) {
+            if (!alphabets.contains(inverse(alphabet))) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private char inverse(char c) {
+        return Character.isLowerCase(c) ? Character.toUpperCase(c) : Character.toLowerCase(c);
+    }
+
+    private Set<Character> getCharacters(String s, int start, int end) {
+        final Set<Character> set = new HashSet<>();
+        for (int index = start ; index <= end ; index++) {
+            set.add(s.charAt(index));
+        }
+        return set;
+    }
+}