給出一個數，倒序輸出它，符號也要考慮，使用整除10和對10的模運算很方便，同時也知道了越界的計算方法

class Solution {
public:
int reverse(int x) {
int rev = 0;
while (x != 0) {
int pop = x % 10;
x /= 10;
if (rev > INT_MAX/10 || (rev == INT_MAX / 10 && pop > 7)) return 0;
if (rev < INT_MIN/10 || (rev == INT_MIN / 10 && pop < -8)) return 0;
rev = rev * 10 + pop;
}
return rev;
}
};

class Solution {
public int reverse(int x) {
int result=0;
try{
String s1="",s2="";
if (x<0){
int y = turn(x);
s1 = Integer.toString(y);
}else{
s1 = Integer.toString(x);
}

while (!"".equals(s1)){
s2+=s1.substring(s1.length()-1);
s1 = s1.substring(0,s1.length()-1);
}
result =Integer.parseInt(s2);
if (x<0){
result = turn(result);
}
}catch (Exception e ){
result = 0;
}
return result;
}

int turn(int a)
{
a = ~a + 1;
return a;
}
}