Leetcode 70. Climbing Stairs

70. Climbing Stairs

• Total Accepted: 120408
• Total Submissions: 321825
• Difficulty: Easy

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?

思路：DP，其实就是斐波那契数列（Fibonacci sequence）。

代码：

class Solution {
public:
    int climbStairs(int n) {
        if(n<1) return 0;
        if(n<=2) return n;
        int one_step_before=2;
        int two_steps_before=1;
        int sum_steps;
        for(int i=3;i<=n;i++){
            sum_steps=one_step_before+two_steps_before;
            two_steps_before=one_step_before;
            one_step_before=sum_steps;
        }
        return sum_steps;
    }
};