LeetCode - Climbing Stairs Java - The Coding Shala

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LeetCode Climbing Stairs Problem

In this post, we will see how to solve the leetcode climbing stairs problem in Java.

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? 
Note: Given n will be a positive integer.

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
Practice on Leetcode Click Here

Climbing Stairs Java Solution

Approach 1:

Using dynamic programming.

Java Program: 

class Solution {
    public int climbStairs(int n) {
        if(n<=2) return n;
        int[] dp = new int[n];
        dp[0] = 1;
        dp[1] = 2;
        for(int i=2;i<n;i++){
            dp[i] = dp[i-1]+dp[i-2];
        }
        return dp[n-1];
    }
}

Approach 2:
Using Recursion.
Java Program: 

class Solution {
    HashMap<Integer, Integer> map = new HashMap<>();
    public int climbStairs(int n) {
        if(map.containsKey(n)){
            return map.get(n);
        }
        
        int result;
        if(n<=2) result = n;
        else{
            result = climbStairs(n-1)+climbStairs(n-2);
        }
        map.put(n,result);
        return result;
    }
}


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