LeetCode70.Climbing Stairs

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?

Note: Given n will be a positive integer.

总结：当递归超时的时候，可以尝试非递归的手段，用一个动态数组保存结果
分析：一开始以为很简单，写了一个斐波那契递归；

class Solution {public:    int climbStairs(int n) {    if(n==0) return 0;        if(n==1) return 1;        if(n==2)  return 2;        return  climbStairs(n-1)+climbStairs(n-2);    }};

结果：Run Code Status: Time Limit Exceeded
所以只能放弃递归了，考虑动态数组保存结果；

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