7. 反转整数(Reverse Integer) C++

知识点：

• 内置变量 INT_MAX   INT_MIN
• 运算结果是否溢出的判断
  • 判断pop>7即pop>INT_MAX%10
  • 判断pop<-8即pop<INT_MIN%10

• class Solution {
  public:
      int reverse(int x) {
          int pop,ans=0;
          while(x)
          {
              pop = x%10;
              x /= 10;
              if(ans > INT_MAX/10 || (ans == INT_MAX/10 && pop >7))
                  return 0;
              if(ans < INT_MIN/10 || (ans == INT_MIN/10 && pop <-8))
                  return 0;
              //cout << "pop: " << pop << " ans: " << ans << '\n';
              ans = ans*10 + pop;
          }
          return ans;
      }
  };