/// <summary>
/// 写一个函数处理字符串，比如输入”I am a girl”,输出”girl a am I”
/// </summary>
/// <param name="p"></param>
/// <returns></returns>
private static string StringConvert(string p)
{
string convertion = null;
Stack stack = new Stack();
int i = 0;
int j = 0;
for (int h = 0; h < p.Length; h++)
{
if (p.Substring(h,1)==" ")
{
j = h;
stack.Push(p.Substring(i,j-i));
i = j + 1;
}
}
stack.Push(p.Substring(i,p.Length-i));
int count = stack.Count;
for (int m = 0; m<count; m++)
{
if (m == 0)
{
convertion = (string)stack.Pop();
}
else
{
convertion = convertion+" " + (string)stack.Pop();
}
}
return convertion;
}
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求两个数的最大公约数【辗转相除法】．
当两个数都较大时，采用辗转相除法比较方便．其方法是：
以小数除大数，如果能整除，那么小数就是所求的最大公约数．否则就用余数来除刚才的除数；再用这新除法的余数去除刚才的余数．依此类推，直到一个除法能够整除，这时作为除数的数就是所求的最大公约数．
例如：求4453和5767的最大公约数时，可作如下除法．
5767÷4453＝1余1314
4453÷1314＝3余511
1314÷511＝2余292
511÷292＝1余219
292÷219＝1余73
219÷73＝3
于是得知，5767和4453的最大公约数是73．
辗转相除法适用比较广，比短除法要好得多，它能保证求出任意两个数的最大公约数．
/// <summary>
/// 辗转相除法:求两个数的最大公约数
/// </summary>
/// <param name="num1"></param>
/// <param name="num2"></param>
/// <returns></returns>
private static int Gcd(int num1, int num2)
{
int gcd=0;
if (num1==num2)
{
gcd = num1;
}
if (num1>num2)
{
int tmp = num1;
num1 = num2;
num2 = tmp;
}
if (num2 % num1 == 0)
{
gcd = num1;
}
else
{
int tmp = num1;
num1 = num2 % num1;
num2 = tmp;
gcd = Gcd(num1, num2);
}
return gcd;
}
P.S: 最小公倍数 = 二数中的大数/最大公约数）*小数
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/// <summary>
/// 求int[]数组里面最大和第二大的数
/// </summary>
/// <param name="max"></param>
/// <param name="second"></param>
/// <param name="a"></param>
private static void MaxAndSecond(ref int max, ref int second, int[]a)
{
max = second = a[0];
for (int i = 0; i < a.Length; i++)
{
if (a[i]>max)
{
second = max;
max = a[i];
}
else if(a[i]>second)
{
second = a[i];
}
}
}
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/// <summary>
/// 求1~N的素数
/// </summary>
/// <param name="p"></param>
private static void PrintPrime(int p)
{
if (p>=2)
{
System.Console.WriteLine("Parime:" + 2);
}
//不需要判断2以外的偶数，因为它们都不是素数，而i从非偶数3开始计数
for (int i = 3; i <= p; i = i + 2)
{
if (IsPrime(i))
{
System.Console.WriteLine("Parime:" + i);
}
}
Console.Read();
}
private static bool IsPrime(int n)
{
//1，2的处理
if (n==1)
{
return false;
}
if (n == 2)
{
return true;
}
//1，2以外的数的处理
else
{
for (int i = 2; i < Math.Sqrt(n) + 1; i++)
{
if (n % i == 0)
return false;
}
}
return true;
}
P.S: 1不是素数。
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/// <summary>
/// 实现一个函数，要求在字符串strA中找出strB出现的次数
/// </summary>
/// <param name="strA"></param>
/// <param name="strB"></param>
/// <returns></returns>
private static int GetSubStrCount(char[] strA, char[] strB)
{
int count = 0;
for (int i = 0; i < strA.Length; i++)
{
int length = 0;
int iA = i;
for (int j = 0; j < strB.Length; j++)
{
if (strB[j] != strA[iA])
{
break;
}
else
{
length = j+1;
iA++;
}
}
if (length==strB.Length)
{
count++;
}
}
return count;
}
