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 public class Solution { 2 public int climbStairs(int n) { 3 // IMPORTANT: Please reset any member data you declared, as 4 // the same Solution instance will be reused for each test case. 5 // s(n) = s(n - 1) + s(n - 2) 6 if(n < 1)return 0; 7 else if(n == 1) return 1; 8 else if(n == 2) return 2; 9 int first = 1; 10 int second = 2; 11 int result = 0; 12 for(int i = 3; i <= n; i ++){ 13 result = first + second; 14 first = second; 15 second = result; 16 } 17 return result; 18 } 19 }
第三遍:
use only 2 constant space:
1 public class Solution { 2 public int climbStairs(int n) { 3 if(n < 1) return 0; 4 int[] result = new int[] { 1, 2 }; 5 for(int i = 2; i < n; i ++){ 6 int tmp = result[0] + result[1]; 7 result[i % 2] = tmp; 8 } 9 return result[(n - 1) % 2]; 10 } 11 }
posted on 2013-11-12 14:24 Step-BY-Step 阅读(129) 评论(0) 编辑 收藏 举报