7. Reverse Integer

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7. Reverse Integer

Description

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-2^31, 2^31 - 1], then return 0.

Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Example 1:

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Input: x = 123
Output: 321

Example 2:

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Input: x = -123
Output: -321

Example 3:

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Input: x = 120
Output: 21

Constraints:

  • -2^31 <= x <= 2^31 - 1

Hints/Notes

  • 2024/12/16
  • digit
  • No solution from 0x3F

Solution

Language: C++

Correct solution:

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