[leetcode] 70. 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?

class Solution {
public:
    int climbStairs(int n) {
        if(n==1) return 1;
        if(n==2) return 2;
        return climbStairs(n-1)+climbStairs(n-2);
    }
};

用递归，显示运行超时。（很多运算重复了）

class Solution {
public:
    int climbStairs(int n) {
        if(n<=2) return n;
        int st[n];
        st[0]=1;
        st[1]=2;
        int i;
        for(i=2;i<n;i++)
        {
            st[i]=st[i-1]+st[i-2];
        }
        return st[n-1];
    }
};

用数组保存，节省堆栈资源