来一个常见的面试题练练手

给定一个数组序列，表示股票的价格，比如说 100 103 109 102 95 101 110 112 103 110 112 112 113 103 103 93 88 94 91 88
现在问你，哪天买入哪天卖出获得的收益最大，输出日期，日期从1开始编号
比如如上序列，结果数5和13，表示95买入113卖出收益最大。

程序的框架已经写好，在solve里面实现，要求时间复杂度是O(n)，一次遍历，并且空间复杂度是O(1)

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;



namespace trade_kadane_problem

{

    class Program

    {

        static int[] GenDataSet(int n)

        {

            int[] result = new int[n];

            Random rnd = new Random();

            int b = 100;

            int u = 200;

            int l = 20;

            int dm = 20;

            for (int i = 0; i < n; i++)

            {

                result[i] = b;

                int r = rnd.Next(dm) - dm / 2;

                if (b + r > u)

                    b = u;

                else if (b + r < l)

                    b = l;

                else

                    b = b + r;

            }

            return result;

        }



        static void Stdsolve(int[] data, out int b, out int s)

        {

            b = 1;

            s = 1;

            for (int i = 0; i < data.Length; i++)

                for (int j = i; j < data.Length; j++)

                {

                    if (data[s - 1] - data[b - 1] < data[j] - data[i])

                    {

                        b = i + 1;

                        s = j + 1;

                    }

                }

        }



        static void solve(int[] data, out int b, out int s)

        {

            b = 1;

            s = 1;

            //在这里编写代码

        }



        static void Print(int[] data)

        {

            for (int i = 0; i < data.Length; i++)

            {

                Console.Write(data[i] + " ");

            }

            Console.WriteLine();

        }



        static void Main(string[] args)

        {

            int[] arr = GenDataSet(20);

            Print(arr);

            int b = 0;

            int s = 0;

            Stdsolve(arr, out b, out s);

            Console.WriteLine("std {0}~{1}", arr[b - 1], arr[s - 1]);

            solve(arr, out b, out s);

            Console.WriteLine("solve {0}~{1}", arr[b - 1], arr[s - 1]);

        }

    }

}

--------------------------------
答案

        static void solve(int[] data, out int b, out int s)

        {

            b = 1;

            s = 1;

            int b1 = b;

            for (int i = 1; i < data.Length; i++)

            {

                if (data[i] < data[b1 - 1])

                    b1 = i + 1;

                if (data[i] - data[b1 - 1] > data[s - 1] - data[b - 1])

                {

                    b = b1;

                    s = i + 1;

                }

            }

        }