题目说明：
Reverse digits of an integer.
Example1: x = 123, return 321
Example2: x = -123, return –321
程序代码：
#include <gtest/gtest.h>
using namespace std; int reverse2(int x)
{
int result[20] = {0};
int resultIdx = 0;
int sign = 1;
long long val = x;
if (val < 0)
{
sign = -1;
val = -val;
} while (val)
{
result[resultIdx++] = val % 10;
val /= 10;
} long long newResult = 0;
long long base = 1;
for (int i = resultIdx-1; i >= 0; i--)
{
newResult += result[i] * base;
base *= 10;
} if (newResult > 0x7FFFFFFF)
{
newResult = 0;
} newResult *= sign; return (int)newResult;
} int reverse(int x)
{
int result[20] = {0};
int resultIdx = 0; while (x)
{
result[resultIdx++] = x % 10;
x /= 10;
} long long newResult = 0;
long long base = 1;
for (int i = resultIdx-1; i >= 0; i--)
{
newResult += result[i] * base;
base *= 10;
} if ((newResult > 0x7FFFFFFF) || (newResult < -0x7FFFFFFF))
{
newResult = 0;
} return (int)newResult;
} TEST(Pratices, tReverse)
{
// 123 -> 321
ASSERT_EQ(reverse(123),321);
// -123 -> -321
ASSERT_EQ(reverse(-123),-321);
// 0 -> 0
ASSERT_EQ(reverse(0),0);
// -0 -> 0
ASSERT_EQ(reverse(-0),0);
// 0x1FFFFFFF -> 0x7FFFFFFF
ASSERT_EQ(reverse(-2147483648),0);
// -0x1FFFFFFF -> -0x7FFFFFFF
//ASSERT_EQ(reverse(-0x1FFFFFFF),-0x7FFFFFFF);
}