7.Reverse-Integer.md

7. Reverse Integer

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题目地址

https://leetcode.com/problems/reverse-integer/

题目描述

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:
Input: 123
Output: 321

Example 2:
Input: -123
Output: -321

Example 3:
Input: 120
Output: 21
Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

代码

Approach #1 Pop and Push Digits & Check before Overflow

class Solution {
  public int reverse(int x) {
    int rev = 0;
    while (x != 0) {
      int pop = x % 10;
      x /= 10;
      if (rev > Integer.MAX_VALUE/10 || (rev == Integer.MAX_VALUE/10 && pop > 7)) return 0;
      if (rev < Integer.MIN_VALUE/10 || (rev == Integer.MIN_VALUE/10 && pop < -8)) return 0;
      rev = rev * 10 + pop;
    }
    return rev;
  }
}