算法：股票交易日

题目描述
在股市的交易日中，假设最多可进行两次买卖(即买和卖的次数均小于等于2)，规则是必须一笔成交后进行另一笔(即买-卖-买-卖的顺序进行)。给出一天中的股票变化序列，请写一个程序计算一天可以获得的最大收益。请采用实践复杂度低的方法实现。

给定价格序列prices及它的长度n，请返回最大收益。保证长度小于等于500。

测试样例：

[10，22，5，75，65，80]，6

返回： 87

package questions;

import java.util.ArrayList;
import java.util.List;

public class StockTradingDay2 {
    private int [] prices;//给定的价格序列；
    private int num ;//价格序列的长度；
    private int count;//一天可以买卖的次数
    private List list;//根据价格生成的新集合

    public void createNode() {
        if(null == prices || prices.length ==0) {
            System.out.println("初始化的价格数组出现错误！");
        }
        if(count<1 || count>num/2) {
            System.out.println("初始化的买卖次数出现错误！");
        }
        list = new ArrayList();
        for(int i =0;i1;i++) {
            for(int j = i+1;jif(prices[j]>prices[i]) {
                    Node node = new Node(i, j, prices[j]-prices[i]);
                    list.add(node);
                }
            }
        }
    }

    public void computeProfits() {
        if(list == null || list.size() ==0) {
            System.out.println("今天不适合进行交易！");
        }
        int n = makeProfits(list);
        System.out.println("最大利润为："+n);
    }

    private int  makeProfits(List tempList) {
        int max = tempList.get(0).getValue();
        List list2 = new ArrayList();
        for(int i =0;iget(i);
            list2.add(n.getValue());
            if(n.getValue()>max) {
                max = n.getValue();
            }

            //从list集合中挑出2个元素，并且元素之间不交叉
            for(int j =0;jget(j);
                if(i != j && n.getStart()for(Integer n : list2) {
            if(n>max) {
                max = n;
            }
        }
        return max ;
    }

    public static void main(String[] args) {
        int [] prices = new int [] {10,22,5,75,65,80};
        StockTradingDay2 st = new StockTradingDay2(prices, 6, 2);
        st.createNode();
        st.computeProfits();

    }
    public StockTradingDay2(int[] prices, int num, int count) {
        super();
        this.prices = prices;
        this.num = num;
        this.count = count;
    }
    public int[] getPrices() {
        return prices;
    }
    public void setPrices(int[] prices) {
        this.prices = prices;
    }
    public int getNum() {
        return num;
    }
    public void setNum(int num) {
        this.num = num;
    }
    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }

    class Node {
        private int start;
        private int end;
        private int value;
        public int getStart() {
            return start;
        }
        public void setStart(int start) {
            this.start = start;
        }
        public int getEnd() {
            return end;
        }
        public void setEnd(int end) {
            this.end = end;
        }
        public int getValue() {
            return value;
        }
        public void setValue(int value) {
            this.value = value;
        }
        public Node(int start, int end, int value) {
            super();
            this.start = start;
            this.end = end;
            this.value = value;
        }
    }
}

———————-分隔线—————–
进阶篇，不限定交易次数

package questions;

import java.util.ArrayList;
import java.util.List;

public class StockTradingDay3 {
    private int [] prices;//给定的价格序列；
    private int num ;//价格序列的长度；
    private int count;//一天可以买卖的次数
    private List list;//根据价格生成的新集合
    //可以认为所有的合理的交易都是为正数的。
    public void createNode() {
        if(null == prices || prices.length ==0) {
            System.out.println("初始化的价格数组出现错误！");
        }
        if(count<1 || count>num/2) {
            System.out.println("初始化的买卖次数出现错误！");
        }
        list = new ArrayList();
        for(int i =0;i1;i++) {
            for(int j = i+1;jif(prices[j]>prices[i]) {
                    Node node = new Node(i, j, prices[j]-prices[i]);
                    list.add(node);
                }
            }
        }
    }

    public void computeProfits() {
        if(list == null || list.size() ==0) {
            System.out.println("今天不适合进行交易！");
        }
        int n = 1;
        do {
            list = makeProfits(list);
            n++;
        }while(n//获取最大的利润
        int max = list.get(0).getValue();
        for(Node nd : list) {
            if(nd.getValue()>max) {
                max = nd.getValue();
            }
        }
        System.out.println("最大利润为："+max);
    }

    private List  makeProfits(List tempList) {
        List newlist =  new ArrayList();
        //使用list是不确定元素个数
        List list2 = new ArrayList();
        for(int i =0;iget(i);
            list2.add(n.getValue());
            newlist.add(n);
            //从list集合中挑出2个元素，并且元素之间不交叉
            for(int j =0;jget(j);
                if(i != j && n.getStart()//如果可以交易多次，是否可以构造新的元素  start = n.getStart()
                    // end = m.getEnd()  value = n.getValue()+m.getValue();
                    //在此基础上，还是找两个元素 
                    list2.add(n.getValue()+m.getValue());
                    Node node = new Node(n.getStart(), m.getEnd(), n.getValue()+m.getValue());
                    newlist.add(node);
                }
            }
        }
        return newlist;

    }

    public static void main(String[] args) {
        int [] prices = new int [] {10,22,5,75,65,80};
        StockTradingDay3 st = new StockTradingDay3(prices, 6, 3);
        st.createNode();
        st.computeProfits();

    }
    public StockTradingDay3(int[] prices, int num, int count) {
        super();
        this.prices = prices;
        this.num = num;
        this.count = count;
    }
    public int[] getPrices() {
        return prices;
    }
    public void setPrices(int[] prices) {
        this.prices = prices;
    }
    public int getNum() {
        return num;
    }
    public void setNum(int num) {
        this.num = num;
    }
    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }

    class Node {
        private int start;
        private int end;
        private int value;
        public int getStart() {
            return start;
        }
        public void setStart(int start) {
            this.start = start;
        }
        public int getEnd() {
            return end;
        }
        public void setEnd(int end) {
            this.end = end;
        }
        public int getValue() {
            return value;
        }
        public void setValue(int value) {
            this.value = value;
        }
        public Node(int start, int end, int value) {
            super();
            this.start = start;
            this.end = end;
            this.value = value;
        }
    }
}