add a solution for 5

fishercoder1534 · fishercoder1534 · commit 90f9a00730c0 · 2022-06-16T17:17:44.000-07:00
diff --git a/src/main/java/com/fishercoder/solutions/_5.java b/src/main/java/com/fishercoder/solutions/_5.java
@@ -60,6 +60,40 @@ private int expand(String s, int left, int right) {
             }
             return r - l - 1;
         }
+    }
+
+    public static class Solution3 {
+        /**
+         * My own implementation using the same idea.
+         */
+        public String longestPalindrome(String s) {
+            String ans = "";
+            int maxLen = 0;
+            for (int i = 0; i < s.length(); i++) {
+                int[] pair = expand(s, i, i);
+                if (pair[1] - pair[0] + 1 > maxLen) {
+                    maxLen = pair[1] - pair[0] + 1;
+                    ans = s.substring(pair[0], pair[1] + 1);
+                }
+                pair = expand(s, i, i + 1);
+                if (pair[1] - pair[0] + 1 > maxLen) {
+                    maxLen = pair[1] - pair[0] + 1;
+                    ans = s.substring(pair[0], pair[1] + 1);
+                }
+            }
+            return ans;
+        }
+
+        private int[] expand(String s, int l, int r) {
+            int[] pair = new int[2];
+            while (l >= 0 && r < s.length() && s.charAt(l) == s.charAt(r)) {
+                pair[0] = l;
+                pair[1] = r;
+                l--;
+                r++;
+            }
+            return pair;
+        }
 
     }
 }
diff --git a/src/test/java/com/fishercoder/_5Test.java b/src/test/java/com/fishercoder/_5Test.java
@@ -9,19 +9,22 @@
 public class _5Test {
     private static _5.Solution1 solution1;
     private static _5.Solution2 solution2;
+    private static _5.Solution3 solution3;
     private static String s;
 
     @BeforeClass
     public static void setup() {
         solution1 = new _5.Solution1();
         solution2 = new _5.Solution2();
+        solution3 = new _5.Solution3();
     }
 
     @Test
     public void test1() {
         s = "babad";
         assertEquals("bab", solution1.longestPalindrome(s));
         assertEquals("aba", solution2.longestPalindrome(s));
+        assertEquals("aba", solution3.longestPalindrome(s));
     }
 
 }
