斐波那契通项公式
斐波那契数列
http://www.nowcoder.com/questionTerminal/c6c7742f5ba7442aada113136ddea0c3
O(1)通项公式解法：
public class Solution {
public int Fibonacci(int n) {
double a = Math.sqrt(5.0);
double temp1 = (1.0 + a)/2.0;
double temp2 = (1.0 - a)/2.0;
return (int)(1.0/a*(Math.pow(temp1, n) - Math.pow(temp2, n)));
}
}
