0070.cpp

class Solution {
public:
    int climbStairs(int n) {
        if (n == 1) return 1;

        vector<int> dp(n + 1);
        dp[1] = 1;
        dp[2] = 2;

        for (int i = 3; i <= n; i++)
            dp[i] = dp[i - 1] + dp[i - 2];

        return dp[n];
    }
};