ReverseInteger done

Author: rampatra

src/main/java/com/leetcode/math/ReverseInteger.java

@@ -0,0 +1,62 @@
+package com.leetcode.math;
+
+/**
+ * Level: Easy
+ * Problem Link: https://leetcode.com/problems/reverse-integer/
+ * Problem Description:
+ * Given a 32-bit signed integer, reverse digits of an integer.
+ * <p>
+ * Example 1:
+ * Input: 123
+ * Output: 321
+ * <p>
+ * Example 2:
+ * Input: -123
+ * Output: -321
+ * <p>
+ * Example 3:
+ * Input: 120
+ * Output: 21
+ * <p>
+ * Note: Assume we are dealing with an environment which could only store integers within the 32-bit signed
+ * integer range: [−2^31,  2^31 − 1]. For the purpose of this problem, assume that your function returns 0 when
+ * the reversed integer overflows.
+ *
+ * @author rampatra
+ * @since 2019-05-31
+ */
+public class ReverseInteger {
+
+    /**
+     * Reverses the input integer.
+     * Time complexity: O(d)
+     * where,
+     * d = number of digits in num
+     * <p>
+     * Runtime: <a href="https://leetcode.com/submissions/detail/232679205/">1 ms</a>.
+     *
+     * @param num an integer.
+     * @return the reverse of {@code num}.
+     */
+    private static int reverse(int num) {
+        long reverse = 0;
+        int pop;
+
+        while (num != 0) {
+            pop = num % 10;
+            num = num / 10;
+            reverse = reverse * 10 + pop;
+        }
+
+        return reverse < Integer.MIN_VALUE || reverse > Integer.MAX_VALUE ? 0 : (int) reverse;
+    }
+
+    public static void main(String[] args) {
+        System.out.println(reverse(0));
+        System.out.println(reverse(-0));
+        System.out.println(reverse(123));
+        System.out.println(reverse(-123));
+        System.out.println(reverse(Integer.MAX_VALUE));
+        System.out.println(reverse(Integer.MIN_VALUE));
+    }
+}