LeetCode 7.Reverse Integer

LeetCode

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 2020/09/22   Share

7. Reverse Integer

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.

Solution

class Solution {
public:
    int reverse(int x) {
       int ans = 0;
       while(x != 0){
           int pop = x % 10;
           x /= 10;
           if(ans > INT_MAX / 10 || ans == INT_MAX / 10 && pop > 7 ) return 0;
           if(ans < INT_MIN / 10 || ans == INT_MIN / 10 && pop < -8 ) return 0;
           ans = ans * 10 + pop;
       }
       return ans;
    }
};

Explanation：

#define INT_MAX = 2147483647

#define INT_MAX = -INT_MAX-1

也就是关于int的最大值和最小值的说明

将一个数字进行反转，从个位数进行取，使用取余的方法，再使用“余数X10”进行往高位移动。

这个过程中需要注意溢出时的条件即可。

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