LeetCode [70] Climbing Stairs

 70. Climbing Stairs

Easy

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?

Example 1:

Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step

 

Constraints:

• 1 <= n <= 45

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//C++ //C++: 0ms class Solution { public: int climbStairs(int n) { if(n<=2) return n; vector<int> dp(n, 0); dp[0] = 1; dp[1] = 2; for(int i=2; i<n; ++i){ dp[i] = dp[i-2]+dp[i-1]; } return dp[n-1]; } }; //Java class Solution { public int climbStairs(int n) { int[] dp = new int[n+1]; dp[0] = 1; dp[1] = 1; for(int i=2; i<=n; ++i){ dp[i] = dp[i-1]+dp[i-2]; } return dp[n]; } }