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.

本质上是dp计算Fibonacci数列：

class Solution {public:    int climbStairs(int n) {        int* dp=(int*)malloc(sizeof(int)*(n+1));        dp[1]=1;        dp[2]=2;        for(int i=3;i<=n;i++)            dp[i]=dp[i-1]+dp[i-2];        return dp[n];    }};

更快一些：

class Solution {public:    int climbStairs(int n) {        if(n==1 || n==2)            return n;        int num1=1, num2=2;        for(int i=3; i<=n; i++)        {            int number = num1+num2;            num1=num2;            num2=number;        }        return num2;    }};