leetcode-70. 爬楼梯

class Solution {
    public int climbStairs(int n) {
        // 少于2个台阶则台阶数与方法一样
        if(n <= 2){
            return n;
        }
        int dp1 = 1, dp2 = 2, dp = 0;
        // dp[n] = dp[n-1] + dp[n-2]
        for(int i = 3;i <= n;i++){
            dp = dp1 + dp2;
            dp1 = dp2;
            dp2 = dp;
        }
        return dp2;
    }
}