【数组】70. 爬楼梯

题目：

 

解答：

d[1] = 1;

d[2] = 2;

再根据公式d[i] = d[i-1] + d[i-2];

class Solution {
public:
    int climbStairs(int n) 
    {
        if (n<=2)
        {
            return n;
        }

        int pre1 = 1;
        int pre2 = 2;
        for (int i=2; i<n; i++) 
        {
            int cur = pre1 + pre2;
            pre1 = pre2;
            pre2 = cur;
        } 
        return pre2;
    }
};