Climbing Stairs

class Solution {
public:
    int findWays(int n, vector<int> &dp)
    {
        if (n <= 1) return 1;
        if (dp[n] != -1) return dp[n];//already solved subproblems
        return dp[n]=findWays(n - 1, dp) + findWays(n - 2, dp); //store the result of subproblem in dp array
    }
    int climbStairs(int n) {
        vector<int>dp(n+1,-1); //fill all values with -1
        return findWays(n,dp);
    }
};