LeetCode--Climbing Stairs

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

递推公式T(n) = T(n-1) + T(n-2);

class Solution 
{
public:
    int climbStairs(int n) 
    {
        int pre;
        int last;
        if(n==0)
            return 0;
        if(n == 1)
            return 1;
        pre=1;
        last=1;
        int res=0;
        for(int i=2; i<=n; i++)
        {
            res = pre+last;
            pre = last;
            last = res;
        }
        return res;
    }
};