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?

思路：递归，f(n)=f(n-1)+f(n-2)，直接用递归超时，改为非递归

代码：

int climbStairs(int n) {
        if(n<=0)
return 0;
int *res=new int[n+1];
memset(res,0,sizeof(int)*(n+1));
res[1]=1;
res[2]=2;
int i=3;
while(i < n+1)
{
res[i]=res[i-1]+res[i-2];
++i;
}
return res[n];
    }