LintCode：Fibonacci

C++

class Solution{
public:
    /**
     * @param n: an integer
     * @return an integer f(n)
     */
    int fibonacci(int n) {
        // write your code here
        int a=0,b=1;
        for (int i=1; i<n; i++) {
            a = a+b;
            b = a-b;
        }
        return a;
    }
};