Java solution 7 && 9

Author: gavinfish

java/_007ReverseInteger.java

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+/**
+ * Reverse digits of an integer.
+ * <p>
+ * Example1: x = 123, return 321
+ * Example2: x = -123, return -321
+ * <p>
+ * Have you thought about this?
+ * Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!
+ * <p>
+ * If the integer's last digit is 0, what should the output be? ie, cases such as 10, 100.
+ * Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer, then the reverse of
+ * 1000000003 overflows. How should you handle such cases?
+ * For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
+ * <p>
+ * Note:
+ * The input is assumed to be a 32-bit signed integer. Your function should return 0 when the reversed integer
+ * overflows.
+ * <p>
+ * Created by drfish on 25/06/2017.
+ */
+public class _007ReverseInteger {
+    public int reverse(int x) {
+        int result = 0;
+        while (x != 0) {
+            int tail = x % 10;
+            int temp = result * 10 + tail;
+            if ((temp - tail) / 10 != result) {
+                return 0;
+            }
+            result = temp;
+            x /= 10;
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        _007ReverseInteger solution = new _007ReverseInteger();
+        assert 321 == solution.reverse(123);
+        assert -321 == solution.reverse(-123);
+        assert 0 == solution.reverse(2147483647);
+    }
+}

java/_009PalindromeNumber.java

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+/**
+ * Determine whether an integer is a palindrome. Do this without extra space.
+ * <p>
+ * Some hints:
+ * Could negative integers be palindromes? (ie, -1)
+ * <p>
+ * If you are thinking of converting the integer to string, note the restriction of using extra space.
+ * <p>
+ * You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that
+ * the reversed integer might overflow. How would you handle such case?
+ * <p>
+ * There is a more generic way of solving this problem.
+ * <p>
+ * Created by drfish on 25/06/2017.
+ */
+public class _009PalindromeNumber {
+    public boolean isPalindrome(int x) {
+        if (x < 0 || (x != 0 && x % 10 == 0)) {
+            return false;
+        }
+        int reverse = 0;
+        while (x > reverse) {
+            reverse = reverse * 10 + x % 10;
+            x /= 10;
+        }
+        return (x == reverse || x == reverse / 10);
+    }
+
+    public static void main(String[] args) {
+        _009PalindromeNumber solution = new _009PalindromeNumber();
+        assert solution.isPalindrome(12321);
+        assert solution.isPalindrome(123321);
+        assert !solution.isPalindrome(-121);
+    }
+}