70. Climbing Stairs

Question

LeetCode Problem

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

Solutions

Use DP

int climbStairs(int n) {
	vector<int> dp(n + 1);
	if (n <= 2) return n;
	dp[0] = 0;
	dp[1] = 1;
	dp[2] = 2;
	for (int i = 3; i <= n; ++i) {
		dp[i] = dp[i-1] + dp[i-2];
	}
	return dp[n];
}