剑指offer 数值的整数次方

题目描述

给定一个double类型的浮点数base和int类型的整数exponent。求base的exponent次方。

/**
     * a^n ={a^(n/2) * a^(n/2),n为偶数;a^(n/2) * a^(n/2) * a}
     *
     * @param base
     * @param exponent
     * @return
     */
    public double Power(double base, int exponent) {
        if (exponent == 0) {
            return 1;
        }
        double res = power(base, Math.abs(exponent));
        return exponent < 0 ? 1.0 / res : res;
    }

    public double power(double base, int exponent) {
        if (exponent == 0) {
            return 1;
        }
        if (exponent == 1) {
            return base;
        }
        double res = power(base, exponent >> 1);
        res *= res;
        if ((exponent & 1) == 1) {//判断exponent是奇数还是偶数
            res *= base;
        }
        return res;
    }