CODE 123. Reverse Integer

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2013/11/12/2013-11-12-CODE 123 Reverse Integer/

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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?
Throw an exception? Good, but what if throwing an exception is not an option? You would then have to re-design the function (ie, add an extra parameter).

public int reverse(int x) {
	// Start typing your Java solution below
	// DO NOT write main() function
	if (x >= -9 && x <= 9) {
		return x;
	}
	boolean ism = x < 0;
	if (ism) {
		x = -x;
	}
	long lx = (long) x;
	int length = 0;
	while (lx > 0) {
		length++;
		lx = lx / 10;
	}
	lx = (long) x;
	for (int i = 0; i <= (length + 1) / 2 - 1; i++) {
		int first = x / (int) Math.pow(10, i) % 10;
		int second = x / (int) Math.pow(10, length - 1 - i) % 10;
		lx = lx - (long) first * (int) Math.pow(10, i);
		lx = lx - (long) second * (int) Math.pow(10, length - 1 - i);
		lx = lx + (long) first * (int) Math.pow(10, length - 1 - i);
		lx = lx + (long) second * (int) Math.pow(10, i);
		if (!ism && lx > Integer.MAX_VALUE) {
			return Integer.MAX_VALUE;
		} else if (ism && lx - 1 > Integer.MAX_VALUE) {
			return Integer.MIN_VALUE;
		}
	}
	return (int) (ism ? -lx : lx);
}