leetcode Climbing Stairs

最近开始刷leetcode的题，一直不太会做动态规划的题目，先找这方面题目做一做，用java。

目前动态规划的题目已经做完，再从易到难总结一下。

Climbing stairs 原题地址：

https://oj.leetcode.com/problems/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?

n阶台阶，一次走一阶或两阶，有多少种不同的走法。

求走到第i阶台阶的走法，等于走到第i-2阶台阶的走法（再一次走两阶）加上走到第i-1阶台阶的走法（再走一阶）。

即f(i) = f(i-2) + f(i-1), i > 2,  f(0) = 0, f(1) = 1, f(2) = 2

public class Solution {    public int climbStairs(int n) {        if (n == 0)        return 0;        if (n == 1)        return 1;        if (n == 2)        return 2;        int a = 1;        int b = 2;        for (int i = 2; i < n; i++) {        int temp = a;        a = b;        b = temp + b;        }        return b;    }}