[题目]
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?
[分析] 一维动态规划入门题
public class Solution { // O(n)空间 public int climbStairs0(int n) { if (n <= 0) return 0; if (n == 1) return 1; int[] dp = new int[n + 1]; dp[1] = 1; dp[2] = 2; for (int i = 3; i <= n; i++) dp[i] = dp[i - 1] + dp[i - 2]; //递推关系式 return dp[n]; } // O(1)空间 public int climbStairs(int n) { if (n <= 0) return 0; int[] dp = {1, 1, 1}; for (int i = 2; i <= n; i++) { dp[2] = dp[1] + dp[0]; dp[0] = dp[1]; dp[1] = dp[2]; } return dp[2]; } }