Solve 10th week problems

Author: bky373

longest-palindromic-substring/bky373.java

@@ -0,0 +1,74 @@
+class Solution {
+
+    /*
+     * Approach 1.
+     * time: O(n^3)
+     * space: O(1)
+     */
+    public String longestPalindrome1(String s) {
+        String longest = "";
+        for (int i = 0; i < s.length(); i++) {
+            for (int j = i; j < s.length(); j++) {
+                String ss = s.substring(i, j + 1);
+                if (isPalindrome(ss)) {
+                    if (ss.length() > longest.length()) {
+                        longest = ss;
+                    }
+                }
+            }
+        }
+        return longest;
+    }
+
+    // Approach 1.
+    private boolean isPalindrome(String s) {
+        int left = 0;
+        int right = s.length() - 1;
+        while (left < right) {
+            if (s.charAt(left) != s.charAt(right)) {
+                return false;
+            }
+            left++;
+            right--;
+        }
+        return true;
+    }
+
+    /*
+     * Approach 2.
+     * time: O(n^2)
+     * space: O(1)
+     */
+    class Solution {
+
+        public String longestPalindrome(String s) {
+            int maxStart = 0;
+            int maxEnd = 0;
+
+            for (int i = 0; i < s.length(); i++) {
+                int start = i;
+                int end = i;
+                while (0 <= start && end < s.length() && s.charAt(start) == s.charAt(end)) {
+                    if (maxEnd - maxStart < end - start) {
+                        maxStart = start;
+                        maxEnd = end;
+                    }
+                    start--;
+                    end++;
+                }
+
+                start = i;
+                end = i + 1;
+                while (0 <= start && end < s.length() && s.charAt(start) == s.charAt(end)) {
+                    if (maxEnd - maxStart < end - start) {
+                        maxStart = start;
+                        maxEnd = end;
+                    }
+                    start--;
+                    end++;
+                }
+            }
+            return s.substring(maxStart, maxEnd + 1);
+        }
+    }
+}