Create LongestPalindrome.java

LongestPalindrome.java

@@ -0,0 +1,57 @@
+class LongestPalindrome {
+    public String longestPalindrome(String s) {
+
+        ArrayList<String> allPalins= new ArrayList<String>();
+        int maxLength = 1;
+        String palindrome = s.substring(0,1);
+        for (Character c: s.toCharArray()) {
+            ListIterator<String> iterator = allPalins.listIterator();
+            // for(String substring: allPalins ) {
+            while(iterator.hasNext()){
+                String substring = iterator.next();
+                iterator.remove();
+                substring = substring+c;
+                iterator.add(substring);
+                // allPalins.add(substring);
+                if(isPalin(substring)) {
+                    if(maxLength<substring.length()) {
+                        maxLength = substring.length();
+                        palindrome = substring;
+                    }
+                }
+            }
+            allPalins.add(c.toString());
+        }
+        return palindrome;
+
+    }
+
+    public boolean isPalin(String substring) {
+        return substring.equalsIgnoreCase(new StringBuilder(substring).reverse().toString());
+    }
+
+    public String idealSolution(String s) {
+      if (s == null || s.length() < 1) return "";
+    int start = 0, end = 0;
+    for (int i = 0; i < s.length(); i++) {
+        int len1 = expandAroundCenter(s, i, i);
+        int len2 = expandAroundCenter(s, i, i + 1);
+        int len = Math.max(len1, len2);
+        if (len > end - start) {
+            start = i - (len - 1) / 2;
+            end = i + len / 2;
+        }
+    }
+    return s.substring(start, end + 1);
+}
+
+private int expandAroundCenter(String s, int left, int right) {
+    int L = left, R = right;
+    while (L >= 0 && R < s.length() && s.charAt(L) == s.charAt(R)) {
+        L--;
+        R++;
+    }
+    return R - L - 1;
+
+    }
+}