非递归斐波那契

求第100个斐波那契数

package utils;

import java.math.BigInteger;

public class FibTest {
public static void main(String[] arags) {
int fibNum = 100;
System.out.println(fib(fibNum));
}

/*
* public static long fib(int n) { if (n < 3) return 1; else { long a = 1;
* long b = 1; for (int i = 2; i < n - 1; i++) { b = a + b; a = b - a;
* System.out.println("a = " + a + " b = " + b); } return a + b; } }
*/

public static BigInteger fib(int n) {
if (n < 3)
return BigInteger.ONE;
else {
BigInteger a = BigInteger.ONE;
BigInteger b = BigInteger.ONE;
for (int i = 2; i < n - 1; i++) {
b = a.add(b);
a = b.subtract(a);
//System.out.println("a = " + a + " b = " + b);
}
return a.add(b);
}
}
}

测试结果：354224848179261915075