public static int climbStairs_dp(int n) {
		 //f(
	        if(n==1)
	            return 1;
	        if(n==2)
	            return 2;
	        int [] steps = new int[n+1];
	        steps[1] = 1;
	        steps[2] = 2;
	        for(int i = 3 ;i<=n;i++){
	            steps[i] = steps[i-1] + steps[i-2];
	        }
			return steps[n];
	    }