7.Reverse Integer_given a signed 32-bit integer x, return x with its-优快云博客

本文介绍如何使用Java反转整数，并详细解释了处理溢出问题的方法，包括针对不同边界条件的考虑。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

题目

Reverse digits of an integer.

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

click to show spoilers.

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.

Update (2014-11-10):
Test cases had been added to test the overflow behavior.

解题思路

用java写非常简单，因为可以轻松实现从String到Integer的转换。需要注意的是溢出问题，如果反转后的整数溢出，函数返回0。

输入int--> Integer-->String -->StringBuffer-->反转-->String-->Integer-->nt。

代码

public int reverse(int x) {
        StringBuffer num=new StringBuffer(Integer.toString(x));	//Integer to StringBuffer
	    int start,end;
	    int i,j;
	    char ch;

	    if(num.charAt(0)>'9'|| num.charAt(0)<'0')
		    start=1;
	    else
		    start=0;
	    end=num.length()-1;

	    i=(start+end)/2;		 //i
	    if((start+end)%2==0)	 //j
		    j=i;
	    else
		    j=i+1;

	    while(i>=start)
	    {
		    ch=num.charAt(i);	//exchange num.charAt(i) with num.charAt(j) 
		    num.setCharAt(i,num.charAt(j));
		    num.setCharAt(j,ch);
		    --i;++j;
	    

		try{
			return Integer.parseInt(num.toString());		//StringBuffer to Integer
		}catch(Exception e){return 0;}
	}