leetcode 70

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?

此题为典型的菲波那切数列问题；

当n=1时，有1种走法；

当n=2时，有2种走法;

当n=3时，有3种走法;

当n=4时，有5种走法；

......

当n=k时，有你n[k-1] + n[k-2]种走法；

代码如下：

class Solution {
public:
    int climbStairs(int n) {
        if(n == 1)
        {
            return 1;
        }
        if(n == 2)
        {
            return 2;
        }
        int a = 1;
        int b = 2;
        int c;
        for(int i = 2; i < n; i++)
        {
            c = a + b;
            a = b;
            b = c;
        }
        return c;
    }
};