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* File: RandomWriter.cpp
* ----------------------
* Name:Zhu Wenjie
* Student ID:517021910799
* This file is the starter project for the random writer problem of Lab 2.
* The project use a model called Markov model, which will determine the future state only related to the current state
* It can be regarded as a state machine, and the current state means the chars before with the size of order which we call them seed
* The state machine will randomly go to one of all the next states (stored in vector)
* and output next char which will change the state by updating the state.
* The project will create a random article based on a text with maxlen of 2000
* Input:
* filename(should be a string)
* order(should be an integer in [0,10]) if you need higher order, it is also legal.
* Output:
* An random article whose initial seed is the most fluent char sequence.
#include <fstream>
#include <iostream>
#include <string>
#include <map>
#include <vector>
#include <ctime>
#include <random>
using namespace std;
#define MAX_CHAR_NUM 2000
ofstream fout("output.txt");
random_device r;
default_random_engine e(r());
// get filename
void read_file(ifstream &fin);
// get order number
int read_order();
// build model
void model_read(ifstream &fin, const int &order, map<string, vector<char>> &model);
// write
void random_write(const int &order, map<string, vector<char>> &model);
void read_file(ifstream &fin)
cout << "Please input your file\n";
//get file name
string filename;
cin >> filename;;
int read_order()
cout << "Please input the order of Markov model\n";
int order;
while (!(cin >> order))
cout << "Try again\n";
char ch;
while ((ch = getchar()) != '\n');//Swallow all wrong input
cin.clear();//reset the fail bit
return order;
void model_read(ifstream &fin, const int &order, map<string, vector<char>> &model)
//store all the character before
string pre;
char ch;
while (fin.get(ch))
//to ensure the seed has enough length
if (pre.size() > order)
//the key for order 0 is all '\0'
if (order == 0)model[""].push_back(ch);
//get seed ending with the last 2 ch with the size of order
string seed(pre.end() - order - 1, pre.end() - 1);
//to prevent EOF condition the ch is not initialized
if (!fin) return;
//add a possibility to the future state of seed
void random_write(const int &order, map<string, vector<char>> &model)
string seed;
unsigned max=0;
//find the most frequent ch
for(auto& x: model){
if (x.second.size() > max) {
max = x.second.size();
seed = x.first;
fout << seed;
int count = seed.size();
//the seed exist and the length of article is shorter than maxlen
while (model.count(seed) != 0 && count <= MAX_CHAR_NUM)
//get all possible output at current state
auto &next = model[seed];
//random sample
uniform_int_distribution<int>u(0, next.size()-1);
char nextch = next[u(e)];
//get the next seed
if (order == 0)seed = "";
else seed = string(seed.begin()+1,seed.end()) + nextch;
fout << nextch;
//update the count of char
int main()
ifstream fin;
while (!fin.is_open())
while (true)
int order = read_order();
map<string, vector<char>> model;
model_read(fin, order, model);
random_write(order, model);
return 0;
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