Climbing Stairs LeetCode solution in Java

1
class Solution {
2
  public int climbStairs(int n) {
3
    int[] memo = new int[n + 1];
4
    return calculateWays(n, memo);
5
  }
6

7
  private int calculateWays(int n, int[] memo) {
8
    if (n == 1 || n == 2) {
9
      return n;
10
    }
11

12
    if (memo[n] != 0) {
13
      return memo[n];
14
    }
15

16
    memo[n] = calculateWays(n - 1, memo) + calculateWays(n - 2, memo);
17
    return memo[n];
18
  }
19
}