[Leetcode] Reverse Integer

Reverse Integer 题解

题目来源：https://leetcode.com/problems/reverse-integer/description/

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Description

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

Example

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 hold integers within the 32-bit signed integer range. 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) {
        long long res = 0;
        while (x) {
            res *= 10;
            res += x % 10;
            x /= 10;
        }
        return (res > INT_MAX || res < INT_MIN) ? 0 : static_cast<int>(res);
    }
};

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解题描述

这道题最关键需要处理的问题就是，原来的输入数字逆向输出的时候会超出int的上限INT_MAX = 2147483647，比如当输入为1534236469，其逆序数为9646324351，显然已经发生了溢出。所以跟atoi同理，要对输出做buffer，上面的解法就用到了long long来做buffer，然后要对输出是否溢出做判断。