1+ package com .leetcode .math ;
2+ 3+ /**
4+ * Level: Easy
5+ * Problem Link: https://leetcode.com/problems/reverse-integer/
6+ * Problem Description:
7+ * Given a 32-bit signed integer, reverse digits of an integer.
8+ * <p>
9+ * Example 1:
10+ * Input: 123
11+ * Output: 321
12+ * <p>
13+ * Example 2:
14+ * Input: -123
15+ * Output: -321
16+ * <p>
17+ * Example 3:
18+ * Input: 120
19+ * Output: 21
20+ * <p>
21+ * Note: Assume we are dealing with an environment which could only store integers within the 32-bit signed
22+ * integer range: [−2^31, 2^31 − 1]. For the purpose of this problem, assume that your function returns 0 when
23+ * the reversed integer overflows.
24+ *
25+ * @author rampatra
26+ * @since 2019年05月31日
27+ */
28+ public class ReverseInteger {
29+ 30+ /**
31+ * Reverses the input integer.
32+ * Time complexity: O(d)
33+ * where,
34+ * d = number of digits in num
35+ * <p>
36+ * Runtime: <a href="https://leetcode.com/submissions/detail/232679205/">1 ms</a>.
37+ *
38+ * @param num an integer.
39+ * @return the reverse of {@code num}.
40+ */
41+ private static int reverse (int num ) {
42+ long reverse = 0 ;
43+ int pop ;
44+ 45+ while (num != 0 ) {
46+ pop = num % 10 ;
47+ num = num / 10 ;
48+ reverse = reverse * 10 + pop ;
49+ }
50+ 51+ return reverse < Integer .MIN_VALUE || reverse > Integer .MAX_VALUE ? 0 : (int ) reverse ;
52+ }
53+ 54+ public static void main (String [] args ) {
55+ System .out .println (reverse (0 ));
56+ System .out .println (reverse (-0 ));
57+ System .out .println (reverse (123 ));
58+ System .out .println (reverse (-123 ));
59+ System .out .println (reverse (Integer .MAX_VALUE ));
60+ System .out .println (reverse (Integer .MIN_VALUE ));
61+ }
62+ }
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