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Assuming that the string is initially empty, the basic operations that can be performed are append/insert/delete/replace, as described below:

append: Appends a string of the specified length to the string.
insert: Inserts a string of the specified length at the specified position of an existing string.
delete: Removes a specified length of characters from an existing string at a specified location.
replace: Replaces a number of characters at a specified position in an existing string with another string.

字符串的位置从 1 开始计数
字符串中的字符，只能是 a-z、A-Z、0-9
每行由一个基本操作+后续参数组成，每种操作的参数不同，用冒号分隔
append：两个参数，分别是要追加字符串的长度、具体的字符串内容
insert：三个参数，分别是插入位置、要插入字符串的长度、具体的内容
delete：两个参数，分别是删除位置，要删除的字符个数
replace：四个参数，分别是替换位置，被替换长度，替换长度，具体的内容

样例：

append : 12 : abcdefghijkl             # 操作完成后，字符串为 "abcdefghijkl"
append : 10 : ABCDEFGHIJ          # 操作完成后，字符串为 "abcdefghijklABCDEFGHIJ"
#insert : 9 : 2 : pq                           # 本行忽略（忽略#开头的行）
insert : 2 : 3 : XYZ                          # 操作完成后，字符串为 "aXYZbcdefghijklABCDEFGHIJ"
delete : 10 : 2                                   # 操作完成后，字符串为 "aXYZbcdefijklABCDEFGHIJ"
replace : 7 : 3 : 10 : 0123456789  # 操作完成后，字符串为 "aXYZbc0123456789ijklABCDEFGHIJ"

代码：

块状链表随便乱搞了一下就好了

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cctype>
#include <cstring>
#include <string>

#define MAXIN 1
#define gc() (SS == TT && (TT = (SS = IN) + fread(IN,1,MAXIN,stdin),SS == TT) ? -1 : *SS++)
int N, qqq;
const int M = 1024 * 1024 * 1 + 5;
int maxsize = 40000, maxnum;

int num, *next, *sz, *pool;
char **data, str[M], IN[MAXIN], *SS = IN, *TT = IN;
char *pre;

inline int read()
{
	int now = 0, f = 1;
	register char c = gc();
	for (; !isdigit(c); c = gc())
		if (c == '-')
			f = -1;
	for (; isdigit(c);
		now = now * 10 + c - '0', c = gc());
	return now * f;
}

inline int new_block()
{
	return pool[++num];
}

inline void del_block(int v)
{
	pool[num--] = v;
}

void init()
{
	for (int i = 1; i < maxnum; ++i)
		pool[i] = i;
	sz[0] = 0;			//新建一个0节点，方便 表头就是0 
	next[0] = -1;
}

void merge(int cur, int Next)
{
	memcpy(data[cur] + sz[cur], data[Next], sz[Next]);
	next[cur] = next[Next];
	sz[cur] += sz[Next];
	del_block(Next);
}

void maintain()
{
	for (int cur = 0, Next = next[0]; ~cur; cur = next[cur], Next = next[cur])
		while ((~Next) && sz[cur] + sz[Next] <= maxsize)
		{
			merge(cur, Next);//最好不用next[Next]，因为已经合并、删掉了
			Next = next[cur];
		}
}

int get_index(int &pos)			//找到pos所在的块，并将pos定位为块内位置 
{
	int cur = 0;
	while ((~cur) && pos > sz[cur])	//把cur定位到某一块的末尾，不用下一块开头了(pos>=sz) 
	{
		pos -= sz[cur];
		cur = next[cur];
	}
	return cur;
}

void update(int cur, int Next, int len, char *s)//给新的块Next设置数据及指针 
{
	next[Next] = next[cur];
	next[cur] = Next;
	sz[Next] = len;
	memcpy(data[Next], s, len);
}

void split(int cur, int pos)
{
	if (cur == -1 || pos == sz[cur])//不能判!pos 因为后边会直接用next[cur]，不分裂会跳过该块
		return;
	int Next = new_block();
	update(cur, Next, sz[cur] - pos, data[cur] + pos);
	sz[cur] = pos;
}

void insert(int pos, int len)
{
	int cur = get_index(pos), sum = 0, Next;
	split(cur, pos);
	while (sum + maxsize <= len)
	{
		Next = new_block();
		update(cur, Next, maxsize, str + sum);//先分成尽可能多的整块 
		sum += maxsize;
		cur = Next;
	}
	if (len - sum)				//剩余的单独放到一块 
		Next = new_block(), update(cur, Next, len - sum, str + sum);
	maintain();
}

void erase(int pos, int len)
{
	int cur = get_index(pos), Next;
	split(cur, pos);
	Next = next[cur];			//because of here
	while ((~Next) && len > sz[Next])
		len -= sz[Next], del_block(Next), Next = next[Next];
	split(Next, len);
	del_block(Next), next[cur] = next[Next];
	maintain();
}

void get_data(int pos, int len)
{
	delete[]pre;
	int cur = get_index(pos), sum = sz[cur] - pos;
	if (len < sum)
		sum = len;
	//memcpy(str, data[cur] + pos, sum);
	fwrite(data[cur] + pos, sizeof(char), sum, stdout);

	cur = next[cur];
	while ((~cur) && sum + sz[cur] <= len)
	{
		//memcpy(str + sum, data[cur], sz[cur]);
		fwrite(data[cur], sizeof(char), sz[cur], stdout);
		sum += sz[cur];
		cur = next[cur];
	}
	if ((~cur) && len - sum)
		fwrite(data[cur], sizeof(char), len - sum, stdout);
	//memcpy(str + sum, data[cur], len - sum);
	//str[len] = '\0';
	//printf("%s", str);
}

bool alloc(int size)
{
	next = new(std::nothrow) int[size];
	if (next == NULL)
		return false;
	sz = new(std::nothrow) int[size];
	if (sz == NULL)
		return false;
	pool = new(std::nothrow) int[size];
	if (pool == NULL)
		return false;

	data = new(std::nothrow) char*[size];
	if (data == NULL)
		return false;
	for (int i = 0; i < size; ++i)
	{
		data[i] = new(std::nothrow) char[maxsize];
		qqq = i;
		if (data[i] == NULL)
			return false;
	}
	return true;
}

int main()
{
	freopen("input.txt", "rb", stdin);
	freopen("output.txt", "wb", stdout);

	fseek(stdin, 0L, SEEK_END);
	N = ftell(stdin);
	fseek(stdin, 0L, SEEK_SET);
	maxnum = N * 2 / maxsize + 100;

	pre = new(std::nothrow) char[M];

	int left = 1, right = maxnum, mid = (left + right) / 2;
	while (1)
	{
		if (left == mid || right == mid)
		{
			maxnum = mid;
			break;
		}
		if (alloc(mid) == true)
		{
			delete[]next;
			delete[]sz;
			delete[]pool;
			for (int i = 0; i < mid; ++i)
				delete[]data[i];
			delete[]data;
			left = mid;
			mid = (left + right) / 2;
		}
		else
		{
			delete[]next;
			delete[]sz;
			delete[]pool;
			for (int i = 0; i < qqq; ++i)
				delete[]data[i];
			delete[]data;
			right = mid;
			mid = (left + right) / 2;
		}
	}

	alloc(maxnum);
	int limit;
	if (maxnum > 200)
		limit = (maxnum - 100)*maxsize / 2;
	else
		limit = 100 * maxsize / 2;

	init();
	int pos = 0, len, tot = 0;
	char c;
	while (1)
	{
		c = gc();
		if (c == -1)
			break;
		if (c == 'a')
		{
			len = read();
			if (len + tot > limit)
			{
				get_data(0, tot);
				return 0;
			}
			while (1)
			{
				char ch = gc();
				if (isdigit(ch) || islower(ch) || isupper(ch))
				{
					str[0] = ch;
					break;
				}
			}
			fread(str + 1, sizeof(char)*(len - 1), 1, stdin);
			insert(tot, len);
			tot += len;
			//get_data(0, tot);

			while (gc() != '\n')
				;
		}
		else if (c == 'i')
		{
			pos = read();
			len = read();
			if (len + tot > limit)
			{
				get_data(0, tot);
				return 0;
			}
			while (1)
			{
				char ch = gc();
				if (isdigit(ch) || islower(ch) || isupper(ch))
				{
					str[0] = ch;
					break;
				}
			}
			fread(str + 1, sizeof(char), len - 1, stdin);
			insert(pos - 1, len);
			tot += len;
			//get_data(0, tot);

			while (gc() != '\n')
				;
		}
		else if (c == 'd')
		{
			pos = read();
			len = read();
			erase(pos - 1, len);
			tot -= len;
			//get_data(0, tot);

		}
		else if (c == 'r')
		{
			pos = read();
			len = read();
			erase(pos - 1, len);
			tot -= len;
			len = read();
			if (len + tot > limit)
			{
				get_data(0, tot);
				return 0;
			}
			tot += len;
			while (1)
			{
				char ch = gc();
				if (isdigit(ch) || islower(ch) || isupper(ch))
				{
					str[0] = ch;
					break;
				}
			}
			fread(str + 1, sizeof(char), len - 1, stdin);
			insert(pos - 1, len);
			//get_data(0, tot);

			while (gc() != '\n')
				;
		}
		else if (c == '#')
			while (gc() != '\n')
				;
	}

	get_data(0, tot);

	fclose(stdout);
	fclose(stdin);
	return 0;
}