438-贪心算法（738.单调递增的数字、714. 买卖股票的最佳时机含手续费、968.监控二叉树）

class Solution {
public:
    int monotoneIncreasingDigits(int n) {
        string str_num = to_string(n);

        int flag = str_num.size();

        for (int i = str_num.size() - 1; i > 0; i--)
        {
            if (str_num[i - 1] > str_num[i])
            {
                flag = i;
                str_num[i - 1]--;
            }
        }

        for (int i = flag; i < str_num.size(); i++)
        {
            str_num[i] = '9';
        }

        return stoi(str_num);
    }
};

class Solution {
public:
    int maxProfit(vector& prices, int fee) {
        int length = prices.size();

        int buy = prices[0] + fee;
        int profit = 0;

        for (int i = 1; i < length; i++)
        {
            if (prices[i] + fee < buy)
            {
                buy = prices[i] + fee;
            }
            else if (prices[i] > buy)
            {
                profit += prices[i] - buy;//局部最优，不一定是最贵的时候卖的！
                buy = prices[i];//为了解决局部最优到全局最优的问题
            }
        }
        return profit;
    }
};