Added task 5.

Author: javadev

src/main/java/s0005.longest.palindromic.substring/Solution.java

@@ -0,0 +1,32 @@
+package s0005.longest.palindromic.substring;
+
+public class Solution {
+    public String longestPalindrome(String s) {
+        int start = 0, end = 0;
+        char[] cs = s.toCharArray();
+        for (int i = 0, max = 0, prev = 0; i < cs.length; ++i) {
+            if (i - max - 1 >= 0 && cs[i - max - 1] == cs[i]
+                    && (prev == i - 1 || isPalindrome(cs, i - max, i))) {
+                start = i - max - 1;
+                end = i + 1;
+                max += 2;
+                prev = i;
+            } else if (isPalindrome(cs, i - max, i + 1)) {
+                start = i - max;
+                end = i + 1;
+                ++max;
+                prev = i;
+            }
+        }
+        return s.substring(start, end);
+    }
+
+    private static boolean isPalindrome(char[] cs, int start, int end) {
+        for (int i = start, j = end - 1; i < j; ++i, --j) {
+            if (cs[i] != cs[j]) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

src/test/java/s0005.longest.palindromic.substring/SolutionTest.java

@@ -0,0 +1,12 @@
+package s0005.longest.palindromic.substring;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+import org.junit.Test;
+
+public class SolutionTest {
+    @Test
+    public void longestPalindrome() {
+        assertThat(new Solution().longestPalindrome("babad"), equalTo("bab"));
+    }
+}