LeetCode-in-All

70. Climbing Stairs

Easy

You are climbing a staircase. It takes n steps to reach the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

Example 1:

Input: n = 2

Output: 2

Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps

Example 2:

Input: n = 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

Constraints:

Solution

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