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?

Note: Given n will be a positive integer.

题目含义：n层高的梯子，每一步能爬1层或2层，问从底爬到顶端有多少种爬法

    public int climbStairs(int n) {
        if (n==1) return 1;
        else if (n==2) return 2;
//        return climbStairs(n-1) + climbStairs(n-2);        //递归方式会超时
        int[] dp = new int[n];
        dp[0] = 1; dp[1] = 2;
        for (int i = 2; i < n; ++i) {
            dp[i] = dp[i - 1] + dp[i - 2];
        }
        return dp[n - 1];  
    }