7.Reverse Integer

Reverse digits of an integer.

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

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.

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思路：注意判错：特别是数值超出，上下溢：“1.绝对值大小必须小于等于numeric_limits<int>::max()” 和“2.如果是最小负数，即numeric_limits<int>::min()，此时不能取反，否则溢出”。

代码：

class Solution {
public:
int reverse(int x) {
if (x==numeric_limits<int>::min()) return 0;
bool negative = false;
long long newx = x;
if (newx == 0){
return 0;
}
else if (newx<0){
negative = true;
newx = -newx;
}
deque<int> mybits;
int remain = 0;
while (newx){
remain = newx % 10;
newx = newx / 10;
mybits.push_front(remain);
}
long long base = 1;
long long result = 0;
for (auto k : mybits){
result += k*base;
base *= 10;
}
if (result>numeric_limits<int>::max()) return 0;
if (negative) return (-1)*result;
else return result;
}
};