70. Climbing Stairs | Leetcode solution

 You are climbing a staircase. It takes n steps to reach 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: n = 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

Input: n = 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

solution:

class Solution {

public:

    vector<int>memo{vector<int>(46, -1)};

    int climbStairs(int n) {

        

        

        if( n == 0)

            return 1;

        else

            if(n < 0)

                return 0;

        if(memo[n] != -1)

            return memo[n];

        int n1 = climbStairs(n-1);

        int n2 = climbStairs(n-2);

        int cp = n1+n2;

        return memo[n] = cp;

        

    }

};