LeetCode Solutions

70. Climbing Stairs

Time: $O(n)$

Space: $O(n)$

			

class Solution {
 public:
  int climbStairs(int n) {
    // dp[i] := # of distinct ways to climb to i-th stair
    vector<int> dp(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];
  }
};
			

class Solution {
  public int climbStairs(int n) {
    // dp[i] := # of distinct ways to climb to i-th stair
    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];
  }
}
			

class Solution:
  def climbStairs(self, n: int) -> int:
    # dp[i] := # Of distinct ways to climb to i-th stair
    dp = [1, 1] + [0] * (n - 1)

    for i in range(2, n + 1):
      dp[i] = dp[i - 1] + dp[i - 2]

    return dp[n]