LeetCode – Refresh – Climbing Stairs

This is pretty simple.

Just use three element to pretain the result;

 

class Solution {
public:
    int climbStairs(int n) {
        vector<int> dp(3, 1);
        for (int i = 2; i <= n; i++) {
            dp[0] = dp[1];
            dp[1] = dp[2];
            dp[2] += dp[0];
        }
        return dp[2];
    }
};