算法面试题

最近到某公司面试后，被问到2个关于算法的题目：

1.最大子段和（一个经典的动态规划算法求解题）

2.已知数据类型栈，请实现队列。

 

代码如下：

 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] a = new int[] { -1, 3, -5, 1, 8, -7, 8, -5, 6, -5, -6 };
            Console.WriteLine("最大子段和是："+MaxSum(a));


            Queue q = new Queue();
            for (int i = 0; i < 10; i++) q.Push(i);
            for (int i = 0; i < 11; i++) Console.WriteLine(q.Pop());
            for (int i = 0; i < 10; i++) q.Push(i);
            for (int i = 0; i < 11; i++) Console.WriteLine(q.Pop());
        }

       /// <summary>
       /// 最大子段和
       /// </summary>
       /// <param name="array"></param>
       /// <returns></returns>
        static int MaxSum(int[] array)
        {
            int b=0;
            int sum=0;
            for (int i = 0; i < array.Length; i++)
            {
                if (b > 0) b += array[i];
                else b = array[i];
                if (sum < b) sum = b;
            }
            return sum;

        }
    }

    /// <summary>
    /// 自定义队列
    /// </summary>
    class Queue
    {
        Stack<int> sa = new Stack<int>();
        Stack<int> sb = new Stack<int>();

        /// <summary>
        /// 将元素插入队列
        /// </summary>
        /// <param name="item"></param>
        public void Push(int item)
        {
            sa.Push(item);
        }

        /// <summary>
        /// 从队列删除并返回一个元素
        /// </summary>
        /// <returns></returns>
        public int? Pop()
        {
            if (IsEmpty()) return null;

            if (sb.Count == 0)
            {
                while (sa.Count > 0) sb.Push(sa.Pop());
                return sb.Pop();
            }
            else return sb.Pop();
        }

        /// <summary>
        /// 判断队列是否为空
        /// </summary>
        /// <returns></returns>
        public bool IsEmpty()
        {
            if (sa.Count == 0 && sb.Count == 0) return true;
            else return false;
        }


    }
}