Fibonacci详解编程语言

Find the Nth number in Fibonacci sequence. 
 
A Fibonacci sequence is defined as follow: 
 
The first two numbers are 0 and 1. 
The i th number is the sum of i-1 th number and i-2 th number. 
The first ten numbers in Fibonacci sequence is: 
 
0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ... 
 
Example 
Given 1, return 0 
 
Given 2, return 1 
 
Given 10, return 34 
 
Note 
The Nth fibonacci number won't exceed the max value of 
signed 32-bit integer in the test cases.

class Solution { 
    /** 
     * @param n: an integer 
     * @return an integer f(n) 
     */ 
    public int fibonacci(int n) { 
        if (n < 0) return -1; 
        if (n == 1) return 0; 
        if (n == 2) return 1; 
 
        int fn = 0, fn1 = 1, fn2 = 0; 
        for (int i = 3; i <= n; i++) { 
            fn = fn1 + fn2; 
            fn2 = fn1; 
            fn1 = fn; 
        } 
 
        return fn; 
    } 
}