leetcode 7. Reverse Integer

Reverse digits of an integer.

Example1: x = 123, return 321
Example2: x = -123, return -321

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Have you thought about this?

Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!

If the integer's last digit is 0, what should the output be? ie, cases such as 10, 100.

Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer, then the reverse of 1000000003 overflows. How should you handle such cases?

For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

 

这道题有两点要注意的，

一个就是如果输入1000，输出是1，而不是0001，

第二个是注意越界的问题，Max Integer是2147483647，但是如果翻转过来，第一位是7，肯定超过了整数的范围，所以在反转过程中要检查是否溢出。

 

当然还有一点值得注意的就是符号的问题。要先转化成long再取绝对值，因为min integer是－2147483648，取绝对值得不到对应的值。

 

public class Solution {
    public int reverse(int x) {
        
        if(x==Integer.MIN_VALUE)  return 0; 
        long result = 0;
        int i = 0;
        
        int temp = (x>0)?1:0;
        x = Math.abs(x);
            
        while(x != 0){
            result *= 10;
            result +=  x%10;
            x /= 10;
            if(result > Integer.MAX_VALUE || result < Integer.MIN_VALUE) return 0;
        }
        return (temp==1)?(int)result:(int)-result;
        
        
    }
}