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how to reverse a number?
Example1: x = 123, return 321 Example2: x = -123, return -321
this is my answer:
public int reverse(int x) {
int result = 0;
while(x != 0){
result = result * 10 + x % 10;
x = x / 10;
}
return result;
}
but when I input 1534236469 , it will output 1056389759 , this is wrong. what do you think about my program? thanks.
379
Reverse an Integer In each iteration of the loop, the remainder when n is divided by 10 is calculated and the value of n is reduced by 10 times. Inside the loop, the reversed number is computed using: reverse = reverse * 10 + remainder; Let us see how the while loop works when n = 2345 .
The inverse of a number A is 1/A since A * 1/A = 1 (e.g. the inverse of 5 is 1/5) All real numbers other than 0 have an inverse. Multiplying a number by the inverse of A is equivalent to dividing by A (e.g. 10/5 is the same as 10* 1/5)
Example: C++ Program to Reverse an Integer. #include <iostream> using namespace std; int main() { int n, reversedNumber = 0, remainder; cout << "Enter an integer: "; cin >> n; while(n != 0) { remainder = n%10; reversedNumber = reversedNumber*10 + remainder; n /= 10; } cout << "Reversed Number = " << reversedNumber; return 0; }
In each iteration, the remainder when the value of n is divided by 10 is calculated, reversedNumber is computed and the value of n is decreased 10 fold. Let us see this process in greater detail: And so on, until n == 0. Finally, the reversedNumber (which contains the reversed number) is printed on the screen.
So if the first character in the string is ‘-’, then the number is negative number, so reverse from index 1 to index length – 1. And finally convert them to integer before returning it, for positive number, simply reverse the string and make it integer before returning.
If the reversed integer overflows, print -1 as the output. Let us see a simple approach to reverse digits of an integer . Attention reader! Don’t stop learning now.
One reason your program cannot give the right answer is that you
store result in an int but you expect to be able to
reverse the number 1534236469.
The correct answer would be 9646324351,
but that number is greater than the largest possible value of an int
so you end up with something else.
Try long long or try using input with no more than 9 digits.
Followup:
I suggested long long because that will fairly reliably give you
an 8-byte integer. You may also get 8 bytes in a long, depending on
where you are building your code,
but Visual C++ on 32-bit Windows (for example) will
give you only 4 bytes. Possibly the 4-byte long will go the way of the 2-byte int soon enough, but at this point in time some of us still have to deal with it.
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