123. Best Time to Buy and Sell Stock III

給予一陣列 prices, prices[i] 代表第 i 天時的股票價錢，回傳我們可以在這幾天中最多可以賺到多少錢，限制最多只能做兩次買進買出。但是你不能同時在還沒賣掉手上股票前，又買入另一天的股票 (手上沒股票時才能買股票)。

Solution

class Solution {
public:
    int maxProfit(vector<int>& prices)
    {
    int t1minCost = INT_MAX, t2minCost = INT_MAX;
    int t1maxProfit = 0, t2maxProfit = 0;

    for (int price : prices)
    {
        t1minCost = min(t1minCost, price);
        t1maxProfit = max(t1maxProfit, price - t1minCost);
        t2minCost = min(t2minCost, price - t1maxProfit);
        t2maxProfit = max(t2maxProfit, price - t2minCost);
    }
    return t2maxProfit;        
    }
};

• 時間複雜度：
  $O(n)$
• 空間複雜度：
  $O(1)$