solution.md

70. Climbing Stairs

Difficulty: Easy

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

Solution

Language: Java

class Solution {
    public int climbStairs(int n) {
        int[] dp = new int[n + 1];
        return this.climbStairs(dp, n);
​
    }
​
    private int climbStairs(int[] dp, int n) {
        if (n <= 1) {
            return 1;
        }
        if (dp[n] > 0) {
            return dp[n];
        }
        int num = climbStairs(dp, n - 1) + climbStairs(dp, n - 2);
        dp[n] = num;
        return num;
    }
}