***(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?

解题思路： 就是斐波那契数列， 递归超时。

class Solution {
    /*int function(int stepsLeft){ // 递归算法，超时
        if(1==stepsLeft)
            return 1;
        if(2==stepsLeft)
            return 2;
        return function(stepsLeft-1)+function(stepsLeft-2);
        
    }*/
public:
    int climbStairs(int n) {
        if(n==0) return 0;
        if(n==1) return 1;
        if(n==2) return 2;
        int p = 1,q=2;
        int tmp = 0 ;
        for(int i = 3 ; i <= n ; i++){ //i表示当前steps
            tmp = p+q;
            p = q ;
            q = tmp;
        }
        return tmp;
    }
};