class Solution {public:    int maxProfit(vector<int> &prices) {        int len = prices.size();        if (len < 2) return 0;        vector<int> i2r(len, 0);        vector<int> i2l(len, 0);        int max_price = prices[len - 1];        for (int i=len-2; i>=0; i--) {            if (prices[i] > max_price) max_price = prices[i];            int cp = max_price - prices[i];            i2r[i] = cp > i2r[i + 1] ? cp : i2r[i + 1];        }        int min_price = prices[0];        for (int i=1; i<len; i++) {            if (prices[i] < min_price) min_price = prices[i];            int cp = prices[i] - min_price;            i2l[i] = cp > i2l[i - 1] ? cp : i2l[i - 1];        }        int mp = 0;        for (int i=0; i<len; i++) {            int p = i2l[i] + i2r[i + 1 >= len ? len - 1 : i + 1];            if (p > mp) mp = p;        }        return mp;    }};