[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?

https://oj.leetcode.com/problems/climbing-stairs/

分析：Fibonacci数列，不要用递推，重复计算太多，用DP。

public class Solution {
    public int climbStairs(int n) {
        if(n<=0)
            return 0;
        if(n==1)
            return 1;
        if(n==2)
            return 2;
        
        int i;
        int firstWays=1;
        int secondWays=2;
        int ways=0;
        for(i=3;i<=n;i++){
            ways=firstWays+secondWays;
            firstWays=secondWays;
            secondWays=ways;
        }
        
        return ways;
            
    }
}