19.2.12 [LeetCode 70] Climbing Stairs

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?

Note: Given n will be a positive integer.

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

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

是用n步到达目的地而不是路有n单位长度