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?

Difficulty: Easy

斐波那契数列。

int climbStairs(int n) {    if(n==1)        return 1;    if(n==2)        return 2;    unsigned long long int pre = 1, curr = 2,temp;    for(int i = 3;i<=n;i++)    {        temp = curr;        curr = curr + pre;        pre = temp;    }    return curr;    }