C++编写算法实现串的置换操作Replace( S, T, R), 即将串S中所有与串T相等的子串置换为串R。

题目：.编写算法实现串的置换操作Replace( S, T, R), 即将串S中所有与串T相等的子串置换为串R。

实现代码：

#include
#include 
using namespace std;
#define MaxSize 100
typedef struct
{	char data[MaxSize];
	int length;			//串长
} SqString;

void StrAssign(SqString &s, char cstr[])	//字符串常量赋给串s
{	int i;
	for (i = 0; cstr[i] != '\0'; i++)
		s.data[i] = cstr[i];
	s.length = i;
}

void DestroyStr(SqString &s)
{  }

void StrCopy(SqString &s, SqString t)	//串复制
{	int i;
	for (i = 0; i < t.length; i++)
		s.data[i] = t.data[i];
	s.length = t.length;
}

bool StrEqual(SqString s, SqString t)	//判串相等
{	bool same = true;
	int i;
	if (s.length != t.length)				//长度不相等时返回0
		same = false;
	else
		for (i = 0; i < s.length; i++)
			if (s.data[i] != t.data[i])	//有一个对应字符不相同时返回0
			{	same = false;
				break;
			}
	return same;
}

int StrLength(SqString s)	//求串长
{	return s.length;
}

SqString Concat(SqString s, SqString t)	//串连接
{	SqString str;
	int i;
	str.length = s.length + t.length;
	for (i = 0; i < s.length; i++)	//将s.data[0..s.length-1]复制到str
		str.data[i] = s.data[i];
	for (i = 0; i < t.length; i++)	//将t.data[0..t.length-1]复制到str
		str.data[s.length + i] = t.data[i];
	return str;
}

SqString SubStr(SqString s, int i, int j)	//求子串
{	SqString str;
	int k;
	str.length = 0;
	if (i <= 0 || i > s.length || j < 0 || i + j - 1 > s.length)
		return str;					//参数不正确时返回空串
	for (k = i - 1; k < i + j - 1; k++)  		//将s.data[i..i+j]复制到str
		str.data[k - i + 1] = s.data[k];
	str.length = j;
	return str;
}

SqString InsStr(SqString s1, int i, SqString s2)	//插入串
{	int j;
	SqString str;
	str.length = 0;
	if (i <= 0 || i > s1.length + 1) //参数不正确时返回空串
		return str;
	for (j = 0; j < i - 1; j++)      		//将s1.data[0..i-2]复制到str
		str.data[j] = s1.data[j];
	for (j = 0; j < s2.length; j++)		//将s2.data[0..s2.length-1]复制到str
		str.data[i + j - 1] = s2.data[j];
	for (j = i - 1; j < s1.length; j++)		//将s1.data[i-1..s1.length-1]复制到str
		str.data[s2.length + j] = s1.data[j];
	str.length = s1.length + s2.length;
	return str;
}

SqString DelStr(SqString s, int i, int j)		//串删去
{	int k;
	SqString str;
	str.length = 0;
	if (i <= 0 || i > s.length || i + j > s.length + 1) //参数不正确时返回空串
		return str;
	for (k = 0; k < i - 1; k++)       		//将s.data[0..i-2]复制到str
		str.data[k] = s.data[k];
	for (k = i + j - 1; k < s.length; k++)	//将s.data[i+j-1..s.length-1]复制到str
		str.data[k - j] = s.data[k];
	str.length = s.length - j;
	return str;
}

SqString RepStr(SqString s, int i, int j, SqString t)	//子串替换
{	int k;
	SqString str;
	str.length = 0;
	if (i <= 0 || i > s.length || i + j - 1 > s.length) //参数不正确时返回空串
		return str;
	for (k = 0; k < i - 1; k++)				//将s.data[0..i-2]复制到str
		str.data[k] = s.data[k];
	for (k = 0; k < t.length; k++)   		//将t.data[0..t.length-1]复制到str
		str.data[i + k - 1] = t.data[k];
	for (k = i + j - 1; k < s.length; k++)	//将s.data[i+j-1..s.length-1]复制到str
		str.data[t.length + k - j] = s.data[k];
	str.length = s.length - j + t.length;
	return str;
}

void DispStr(SqString s)	//输出串s
{	int i;
	if (s.length > 0)
	{	for (i = 0; i < s.length; i++)
			printf("%c", s.data[i]);
		printf("\n");
	}
}


void Getbiaohaoxiazhi(SqString t, int nextval[])
{	int j = 0, k = -1;
	nextval[0] = -1;
	while (j < t.length)
	{	if (k == -1 || t.data[j] == t.data[k])
		{	j++;
			k++;
			if (t.data[j] != t.data[k])
				nextval[j] = k;
			else
				nextval[j] = nextval[k];

		}
		else
			k = nextval[k];
	}
}

int KMPIndex1(SqString s, SqString t)
{	int nextval[MaxSize], i = 0, j = 0;
	Getbiaohaoxiazhi(t, nextval);
	while (i < s.length && j < t.length)
	{	if (j == -1 || s.data[i] == t.data[j])
		{	i++;
			j++;
		}
		else
			j = nextval[j];

	}
	if (j >= t.length)
		return (i - t.length);
	else
		return -1;
}

SqString Repalce(SqString S, SqString T, SqString R)
{	int i, flag = 1; //用于保存与串T相等的S串的下标起始值
	SqString str, str1; //str 返回值;str1 变动串
	str.length = 0;
	StrCopy(str1, S); //在str1上进行改动
	while (flag)
	{	i = KMPIndex1(str1, T);
		if (i == -1)
		{	flag = 0;
			break;//串S中没有与T相等的子串，退出
		}
		str = Concat(str, SubStr(str1, 1, i)); //第一次时将str1之前的字符连接在str上;第一次以后因为有修改str1.
		str = Concat(str, R); //连接替换内容
		StrCopy(str1, SubStr(str1, i + T.length + 1, str1.length - (i + T.length))); //将i+T.length之前的字符删去
	}

	str = Concat(str, str1); //循环中找不到等于T的子串后，将剩下的str1加到str尾部
	return str;
}

int main()
{	SqString S, T, R;
	char s[] = "我拿红豆比作友情，你拿红豆比作爱情。";
	char t[] = "红豆";
	char r[] = "长亭";
	StrAssign(S, s);
	StrAssign(T, t);
	StrAssign(R, r);
	SqString str;
	printf("串S:");DispStr(S);
	printf("串T:");DispStr(T);
	printf("串R:");	DispStr(R);
	str = Repalce(S, T, R);
	printf("替换后:");	DispStr(str);
	return 0;
}