class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int n = prices.size();
        if(n==1) return 0;
        int f[n][3];
        memset(f,-0x3f,sizeof f);
        f[0][0] = -prices[0];
        f[0][1] = 0;
        f[0][2] = 0;
        for(int i=1;i<n;i++)
        {
            f[i][0] = max(f[i-1][0],f[i-1][2]-prices[i]);
            f[i][1] = f[i-1][0]+prices[i];
            f[i][2] = max(f[i-1][2],f[i-1][1]);
        }
        return max(f[n-1][1],f[n-1][2]);
    }
};