面试题(C#算法编程题)

1>用C#写一段选择排序算法，要求用自己的编程风格。
答：private int min;
public void xuanZhe(int[] list)//选择排序
{
for (int i = 0; i < list.Length - 1; i++)
{
min = i;
for (int j = i + 1; j < list.Length; j++)
{
if (list[j] < list[min])
min = j;
}
int t = list[min];

list[min] = list[i];

list[i] = t;
}
}

首先是二分查找法，时间复杂度O（2log2（n））：
static bool Find(int[] sortedArray, int number)
{
if (sortedArray.Length == 0)
return false;

int start = 0;
int end = sortedArray.Length - 1;

while (end >= start)
{
int middle = (start + end) / 2;
if (sortedArray[middle] < number)
start = middle + 1;
else if (sortedArray[middle] > number)
end = middle - 1;
else
return true;
}
return false;
}

然后是三分查找算法，时间复杂度O（3log3（n））：
static bool Find(int[] sortedArray, int number)
{
if (sortedArray.Length == 0)
return false;

int start = 0;
int end = sortedArray.Length - 1;

while (end >= start)
{
int firstMiddle = (end - start) / 3 + start;
int secondMiddle = end - (end - start) / 3;
if (sortedArray[firstMiddle] > number)
end = firstMiddle - 1;
else if (sortedArray[secondMiddle] < number)
start = secondMiddle + 1;
else if (sortedArray[firstMiddle] != number && sortedArray[secondMiddle] != number)
{
end = secondMiddle - 1;
start = firstMiddle + 1;
}
else
return true;
}
return false;
}

2>一列数的规则如下: 1、1、2、3、5、8、13、21、34...... 求第30位数是多少， 用递归算法实现。
private static int Digui(int j)
{
if (j<=0)
return 0;
if (j == 1)
return 1;
return Digui(j-1) + Digui(j - 2);
}

1+2………………n
private static int Digui1(int j)
{
if (j == 0)
return 0;
return Digui1(j - 1) + j;
}

写一个函数计算当参数为N的值:1-2+3-4+5-6+7……+N
答：public int returnSum(int n)
{
int sum = 0;
for (int i = 1; i <= n; i++)
{
int k = i;
if (i % 2 == 0)
{
k = -k;
}
sum = sum + k;
}
return sum;

}

public int returnSum1(int n)
{
int k = n;
if (n == 0)
{
return 0;
}
if (n % 2 == 0)
{
k = -k;
}
return aaa(n - 1) + k;
}

3>20个随机数列
Dictionary<string, int[]> dict = new Dictionary<string, int[]>();

ArrayList newArray;
int[] intArray;
Random rd;

while (dict.Count < 20)
{
intArray = new int[5];
rd = new Random();
newArray = new ArrayList();
while (newArray.Count < 5)
{
int tempNumber = rd.Next(0, 10);
if (!newArray.Contains(tempNumber))
newArray.Add(tempNumber);
}
string str=ArrayConvertToString(newArray);
for (int i = 0; i < 5; i++)
{
intArray[i] = (int)newArray[i];
}
if (!dict.ContainsKey(str))
{
dict.Add(str, intArray);
}
}

foreach (var l in dict)
{
Console.WriteLine(l.Key);
}
Console.WriteLine("@@" + dict.Keys.Max() + "@@" + dict.Keys.Min());
Console.ReadKey();
}

static public string ArrayConvertToString(ArrayList al)
{
string strTemp=string.Empty;
foreach (var aList in al)
{
strTemp += aList;
}
return strTemp;
}

4>

public abstract class A
{
public A()
{
Console.WriteLine('A');
}
public virtual void Fun()
{
Console.WriteLine("A.Fun()");
}
}

public class B : A
{
public B()
{
Console.WriteLine('B');
}
public new void Fun()
{
Console.WriteLine(" B.Fun()");
}
public static void Main()
{
A a = new B();
a.Fun();
Console.Read();
}
A B A.fun()

public class A
{
public virtual void Fun1(int i)
{
Console.WriteLine(i);
}
public void Fun2(A a)
{
a.Fun1(1);
Fun1(5);
}
}
public class B : A
{
public override void Fun1(int i)
{
base.Fun1(i + 1);
}
public static void Main()
{
A a = new A();
B b = new B();
a.Fun2(b);
b.Fun2(a);
Console.Read();
}
}

2 5 1 6

6. 写出程序的输出结果
class Class1 {
private string str = "Class1.str";
private int i = 0;2
static void StringConvert(string str) {
str = "string being converted.";
}
static void StringConvert(Class1 c) {
c.str = "string being converted.";
}
static void Add(int i) {
i++;
}
static void AddWithRef(ref int i) {
i++;
}
static void Main() {
int i1 = 10;
int i2 = 20;
string str = "str";
Class1 c = new Class1();
Add(i1);
AddWithRef(ref i2);21
Add(c.i);
StringConvert(str);
StringConvert(c);
Console.WriteLine(i1);
Console.WriteLine(i2);
Console.WriteLine(c.i);
Console.WriteLine(str);
Console.WriteLine(c.str);
}
}
答：10，21，0，str，string being converted.

10. 程序设计: 猫大叫一声，所有的老鼠都开始逃跑，主人被惊醒。(C#语言)
要求： 1.要有联动性，老鼠和主人的行为是被动的。
2.考虑可扩展性，猫的叫声可能引起其他联动效应。
public interface Observer
{
void Response(); //观察者的响应，如是老鼠见到猫的反映
}
public interface Subject
{
void AimAt(Observer obs); //针对哪些观察者，这里指猫的要扑捉的对象---老鼠
}
public class Mouse : Observer
{
private string name;
public Mouse(string name, Subject subj)
{
this.name = name;
subj.AimAt(this);
}

public void Response()
{
Console.WriteLine(name + " attempt to escape!");
}
}
public class Master : Observer
{
public Master(Subject subj)
{
subj.AimAt(this);
}

public void Response()
{
Console.WriteLine("Host waken!");
}
}

public class Cat : Subject
{
private ArrayList observers;
public Cat()
{
this.observers = new ArrayList();
}
public void AimAt(Observer obs)
{
this.observers.Add(obs);
}
public void Cry()
{
Console.WriteLine("Cat cryed!");
foreach (Observer obs in this.observers)
{
obs.Response();
}
}
}
class MainClass
{
static void Main(string[] args)
{
Cat cat = new Cat();
Mouse mouse1 = new Mouse("mouse1", cat);
Mouse mouse2 = new Mouse("mouse2", cat);
Master master = new Master(cat);
cat.Cry();
}
}

//---------------------------------------------------------------------------------------------
设计方法二: 使用event -- delegate设计..
public delegate void SubEventHandler();
public abstract class Subject
{
public event SubEventHandler SubEvent;
protected void FireAway()
{
if (this.SubEvent != null)
this.SubEvent();
}
}
public class Cat : Subject
{
public void Cry()
{
Console.WriteLine("cat cryed.");
this.FireAway();
}
}
public abstract class Observer
{
public Observer(Subject sub)
{
sub.SubEvent += new SubEventHandler(Response);
}
public abstract void Response();
}
public class Mouse : Observer
{
private string name;
public Mouse(string name, Subject sub) : base(sub)
{
this.name = name;
}
public override void Response()
{
Console.WriteLine(name + " attempt to escape!");
}
}
public class Master : Observer
{
public Master(Subject sub) : base(sub){}
public override void Response()
{
Console.WriteLine("host waken");
}
}
class Class1
{
static void Main(string[] args)
{
Cat cat = new Cat();
Mouse mouse1 = new Mouse("mouse1", cat);
Mouse mouse2 = new Mouse("mouse2", cat);
Master master = new Master(cat);
cat.Cry();
}
}