leetcode-algorithms-7 Reverse Integer

leetcode-algorithms-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.

解法

反复求余数,对余数乘10.

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

时间复杂度: O(lg(x)).
空间复杂度: O(1).

链接: leetcode-algorithms 目录