class Solution {
public:
    int minCostClimbingStairs(vector<int>& cost) {
        int len=cost.size();
        vector<int> dp(len+1);
        dp[0]=dp[1]=0;
        for(int i=2;i<=len;++i)
        {
            dp[i]=min(dp[i-1]+cost[i-1],dp[i-2]+cost[i-2]);
        }
        return dp[len];
    }
};

class Solution {
public:
    int minCostClimbingStairs(vector<int>& cost) {
        int len=cost.size();
        int a=0,b=0,m=0;
        for(int i=2;i<=len;++i)
        {
            m=min(a+cost[i-2],b+cost[i-1]);
            a=b;
            b=m;
        }
        return m;
    }
};