java - 反转 int 限制内的整数值

Question

我想反转一个整数。我尝试了以下代码，当数字太大以至于它的反向大于 int 限制(例如 1534236469)时会出现问题，因此在这种情况下它会返回一些垃圾整数。

如何使用 Integer.MIN_VALUE 和 Integer.MAX_VALUE 检查反转后的数字是否在限制范围内？

注意:只能使用int变量类型。

int num = 1534236469;

int reverseInt = 0;
int multiplier = 1;

if ( num < 0 ) {
    multiplier *= -1;
}

while ( num != 0 ) {

    //get the last digit
    int digit = num % 10;

    //multiply the reverseInt by 10 and then add the last digit
    reverseInt = (reverseInt * multiplier) + digit;

    multiplier = 10;
    num /= 10;
}

//how to fix this.
if (reverseInt < Integer.MIN_VALUE || reverseInt > Integer.MAX_VALUE ) {
    System.out.println("Invalid number");
} else {
    System.out.println("Reversed integer is " + reverseInt);
        }

Answer 1

您只需在添加下一个数字之前进行检查，这样您就可以简单地将检查移至实际计算中。如果您当前的反向正数大于 Integer.MAX_VALUE/10，则您无法添加其他数字。负数也是如此。

我唯一做的就是将你的这部分代码移上去:

if (reverseInt < Integer.MIN_VALUE || reverseInt > Integer.MAX_VALUE ) {
    System.out.println("Invalid number");
} else {

然后我添加了 /10 和一个 return 语句，因为程序必须在溢出时结束:

public class StackOverflowTest {
  public static void main(String[] args) {
    int num = -1534236469;

    int reverseInt = 0;
    int multiplier = 1;

    if ( num < 0 ) {
        multiplier *= -1;
    }

    while ( num != 0 ) {

        // if this next step will push is into overflow, then stop:
        if (reverseInt < Integer.MIN_VALUE/10 || reverseInt > Integer.MAX_VALUE/10) {
          System.out.println("Invalid number");
          return;

        } else {

          //get the last digit
          int digit = num % 10;

          // multiply the reverseInt by 10 and then add the last digit
          reverseInt = (reverseInt * multiplier) + digit;
        }

        multiplier = 10;
        num /= 10;
    }

    System.out.println("Reversed integer is " + reverseInt);
  }
}

---

或者，您可以将其视为字符串，然后简单地反转字符串(连同符号摆弄):

public class StackOverflowTest {
  public static void main(String[] args) {

    reverse(1534236469);
    System.out.println();
    reverse(-153423646);
  }

  public static void reverse(int num) { 
    System.out.println("int = " + num);
    int number = num < 0 ? -num : num;           // remove the sign

    String reverse = new StringBuilder(String.valueOf(number)).reverse().toString();
    System.out.println("reverse String: " + reverse);

    try {
      int reversed = Integer.parseInt(reverse);
      reversed = num < 0 ? -reversed : reversed;  // get back the sign
      System.out.println("Reversed integer is " + reversed);
    } catch (NumberFormatException ex) {
      System.out.println("Invalid number");
    }
  }
}

打印:

int = 1534236469
reverse String: 9646324351
Invalid number

int = -153423646
reverse String: 646324351
Reversed integer is -646324351