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;
  }
  }