LintCode-111.爬楼梯

public class Solution {
    /**
     * @param n: An integer
     * @return: An integer
     */
    public int climbStairs(int n) {
        // write your code here
        if(n  == 0) return 0;
        else if(n == 1) return 1;
        else if(n == 2) return 2;
        else{
            int a = 1, b =2, c = 0;
            for (int i = 0; i < n - 2; i++ ){
                c = a + b; a = b;b = c;
            }
            return c;
        }
    }
}