乘方--java递归实现--循环实现

package recursion;

//计算乘方
public class Power {
static long temp=1;
//--------递归实现乘方计算，时间O(logN)---------

public long calculate(long x, int y) {

if (y == 1) {
return x * temp;
}
if (y == 2) {
return (x * x * temp);
}
if (y % 2 == 1) {
temp = x;
}

return calculate(x * x, y / 2);

}

// ------------递归实现乘方，时间O（N）------------------------
public long calculate2(long x, int y) {
if (y == 1) {
return x;
} else
return x * calculate2(x, y - 1);
}
//--------------循环实现乘方，时间O（N）------------------
public long calculate3(long x, int y) {
long result = 1;
for (int i = 0; i < y; i++) {
result = result * x;
}
return result;
}

}

2.测试程序

import recursion.Power;

public class App {

/**
* @param args
*/
public static void main(String[] args) {
Power power = new Power();
long result = power.calculate(5, 10);
System.err.println(result);
// ----------------------------
result = power.calculate2(5, 10);
System.err.println(result);
// --------------------
result = power.calculate3(5, 10);
System.err.println(result);
}

}

3.测试结果

9765625
9765625
9765625