public class Solution {public int maxProfit(int[] prices) {// Start typing your Java solution below// DO NOT write main() functionif (prices.length == 0 || prices.length == 1) return 0;int ans = 0;int max = 0;int len = prices.length;int historyProfit[] = new int[len];int futureProfit[] = new int[len];int valley  = prices[0];for (int i = 1; i < len; i++) {if (prices[i] >= prices[i-1]) {int val = prices[i] - valley ;if (val > max) max = val;             }else {if (prices[i] < valley ) valley  = prices[i];}historyProfit[i] = max;}       int peek = prices[len - 1];ans = max;max = 0;for (int i = len - 2; i >= 1; i--) {if (prices[i+1] >= prices[i]) {int val = peek - prices[i];if (val > max) max = val;}else {if (prices[i] > peek) peek = prices[i];}futureProfit[i] = max;int p = futureProfit[i] + historyProfit[i-1];if (p > ans) {ans = p;}}return ans;}
}

class Solution {
public:int maxProfit(vector<int> &prices) {// null checkint len = prices.size();if (len==0) return 0;vector<int> historyProfit;vector<int> futureProfit;historyProfit.assign(len,0);futureProfit.assign(len,0);int valley = prices[0];int peak = prices[len-1];int maxProfit = 0;// forward, calculate max profit until this timefor (int i = 0; i<len; ++i){valley = min(valley,prices[i]);if(i>0){historyProfit[i]=max(historyProfit[i-1],prices[i]-valley);}}// backward, calculate max profit from now, and the sum with historyfor (int i = len-1; i>=0; --i){peak = max(peak, prices[i]);if (i<len-1){futureProfit[i]=max(futureProfit[i+1],peak-prices[i]);}maxProfit = max(maxProfit,historyProfit[i]+futureProfit[i]);}return maxProfit;}
};