最简单的DP!

class Solution {
    /**
     * 最简单的DP!
     */
    public int climbStairs(int n) {
        int[] f = new int[n+2];
        f[0] = 0;
        f[1] = 1;
        for (int i = 0; i < n; i++) {
            f[i+2] = f[i] + f[i+1];
        }
        return f[n+1];
    }
}