July - Day 31 - Climbing Stairs

Solution.java

// https://leetcode.com/explore/challenge/card/july-leetcoding-challenge/548/week-5-july-29th-july-31st/3407/

import java.util.*;

public class Solution {
    TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
    
    public int climbStairs(int n) {
        
        if(n == 0)
            return 1;
        if(n < 0)
            return 0;
        if(map.containsKey(n))
            return map.get(n);
        
        int left = climbStairs(n - 1);
        int right = climbStairs(n - 2);
        int sum = left + right;
        map.put(n, sum);
        
        return sum;
    }
}