LeetCode 70 Climbing Stairs - Easy

70. Climbing Stairs — Easy

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Problem

70. Climbing Stairs -- 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?

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

Constraints: 1 <= n <= 45

Solution

### DP:
class Solution:
    def climbStairs(self, n: int) -> int:
        if n < 2:
            return 1
        # Let dp[i]dp[i] denotes the number of ways to reach on ith step
        dp = [0] * (n + 1)
        dp[1] = 1
        dp[2] = 2
        for i in range(3, n + 1):
            dp[i] = dp[i - 1] + dp[i - 2]
        return dp[n]