爬楼梯

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