Reverse Integer
Given a 32-bit signed integer, reverse the digits of an integer.
Constraints:
- Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−2^31, 2^31 − 1].
- For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
Examples:
Input: 123
Output: 321
Explanation: The reverse of 123 is 321.
Input: -123
Output: -321
Explanation: The reverse of -123 is -321.
Input: 120
Output: 21
Explanation: The reverse of 120 is 21.
Solutions
Mathematical Approach
Time: O(log|x|)Space: O(1)
The solution works by first determining the sign of the input number. Then it iterates over each digit of the number from right to left, appending it to the result. If the result exceeds the 32-bit signed integer range, it returns 0.
function reverse(x) {
let sign = x < 0 ? -1 : 1;
x *= sign;
let res = 0;
while (x > 0) {
let digit = x % 10;
x = Math.floor(x / 10);
res = res * 10 + digit;
if (res > 2**31 - 1 || res < -2**31) return 0;
}
return sign * res;
}Follow-up:
How would you optimize the solution for very large integers?
