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?
1 自己的代码：运行并不成功，相对于对每个小于n的元素进行了两倍的操作，超时。

package leetcode;

public class ClimbingStairs {
	public int climbStairs(int n) {
		if(n == 1) return 1;
		if(n == 2) return 2;
		int sum = 0;
		if(n > 2){
			sum += climbStairs(n - 1) + climbStairs(n - 2);
		}
        return sum;
    }
}

2 动态规划代码

package leetcode;

public class ClimbingStairs {
	
	public int climbStairs(int n) {
		if(n == 1) return 1;
		if(n == 2) return 2;
		int returns = 0;
		if(n > 2){
			int[] sum = new int[n+1];
			sum[1] = 1;
			sum[2] = 2;
			for(int i = 3; i < n+1; i++)
				sum[i] = sum[i-1] + sum[i-2];
			returns = sum[n];
		}
        return returns;
    }
	
}