题目:实现函数double power(double base, int exponent),求base的exponent次方。不得使用库函数,同时不需要考虑大数问题。
思路:先判断指数大小,分为正数,0和负数三种情况,分别处理。计算平方的时候,运用斐波那契原理减少重复计算。
解决方案:
public class Question16 {
private static boolean invalidInput = false;
public static double Power(double base, int exponent) {
invalidInput = false;
double result;
if (exponent > 0){
result = PowerWithUnsignedExponent(base, exponent);
} else if (exponent < 0){
if (base == 0){
invalidInput = true;
return 0.0;
}
result = 1 / PowerWithUnsignedExponent(base, -exponent);
}else {
return 1;
}
return result;
}
private static double PowerWithUnsignedExponent(double base, int exponent) {
if (exponent == 0) {
return 1;
}
if (exponent == 1) {
return base;
}
double result = PowerWithUnsignedExponent(base, exponent >> 1);
result *= result;
if ((exponent & 0x1) == 1) {
result *= base;
}
return result;
}
public static void main(String[] args) {
System.out.println(Power(5, 2));
}
}
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