在计算幂时使用int，double和long

Question

我在弄清楚什么时候使用int，double和long时遇到麻烦。

我正在计算整数的幂并返回结果，只要提供的幂不是负数即可。

对于作业，我需要使用以下代码开始：

public static long powerN(int number, int power) {

这是我想出的：

public class PowerCalculator
{
/**
 * Calculate the non-negative power of an integer number. If a negative power is input, the method returns 1.
 * 
 * @param number The number to take power.
 * @param power The power factor to be taken to.
 * @return The calculation result after taking power of the integer number.
 */
    public static long powerN(int number, int power) {

       if (power > 0)
       {  
         double result = (Math.pow(number, power));  
         return result; 
       }
       else 
       {
         return 1; 
       }
    }
}

我知道我正在弄乱使用int，double或long的方法，但是我不知道如何解决它。

Answer 1

等待！ 如果您自己进行操作，请使用更快的算法，例如通过平方来求幂 ，如下所示：

long powerN(long number, int power){
    long res = 1;
    long sq = number;
    while(power > 0){
        if(power % 2 == 1){
            res *= sq; 
        }
        sq = sq * sq;
        power /= 2;
    }
    return res;
}

Answer 2

您可以自己做：

public static long powerN(
   int number, 
   int power
) {
   if(power == 0) return 1;
   int result = number;

   while(power > 1) {
      result*=number;
      power--;
   }

   return (long)result;
}

PS：这不能处理负电源。

Answer 3

如果您想使用Math.pow ：

public static long powerN(int number, int power) {
  return (long) Math.pow(number, power);
}

Answer 4

选项1：将Math.pow的结果强制转换为long：

public class PowerCalculator{
/**
 * Calculate the non-negative power of an integer number. If a negative power is input, the method returns 1.
 * 
 * @param number The number to take power.
 * @param power The power factor to be taken to.
 * @return The calculation result after taking power of the integer number.
 */
public static long powerN(int number, int power) {

    // write your code after this line
    if (power < 0){
        return 1;
    } else{
        return (long) Math.pow(number, power);
    }

选项2：不使用Math.pow

    public class PowerCalculator{
/**
 * Calculate the non-negative power of an integer number. If a negative power is input, the method returns 1.
 * 
 * @param number The number to take power.
 * @param power The power factor to be taken to.
 * @return The calculation result after taking power of the integer number.
 */
public static long powerN(int number, int power) {

    // write your code after this line
    long result = 1;
    while (power > 0) {
        result *= number;
        power--;
    }
    return result;
}