070 - Climbing Stairs

70. Climbing Stairs

Problem Statement:

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:

• 1 <= n <= 45

Solution:

Java

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

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