Solve linear equation with Maps - c++

Question

I have almost completed the coding to solve simple linear equation set. Just seem to missing something in the recursive call with Maps causing issue.
Here is the problem statement to solve, example:
X = Y + 2
Y = Z + R + 1
R = 2 + 3
Z = 1
Given: LHS would be just variable names. RHS would have only variables, unsigned int and '+' operator. Solve for all unknowns.
Solution that I get with my code:
X = 2
Y = 1
R = 5
Z = 1
My code :
#include <vector>
#include <string>
#include <sstream>
#include <iostream>
#include <map>
#include <fstream>
#include <set>
#include <regex>
using namespace std;
map<string, string> mymap;
// Method to Parse a given expression based on given arg delimiter
// ret: vector of parsed expression
vector<string> parse_expr(string n, char *delims)
{
vector<string> v;
string cleanline;
char* char_line = (char*)n.c_str(); // Non-const cast required.
char* token = NULL;
char* context = NULL;
vector<string>::iterator it;
token = strtok_s(char_line, delims, &context);
while (token != NULL)
{
cleanline += token;
cleanline += ' ';
v.push_back(token);
token = strtok_s(NULL, delims, &context);
}
return v;
}
//Method to find sum for a given vector
//retype: string
//ret: sum of given vector
string find_VctrSum(string key, vector<string> v)
{
int sum = 0;
string val;
vector<string>::iterator i;
for (i = v.begin(); i != v.end(); i++)
{
val = *i;
//cout << "val is :" << val << endl;
sum += stoi(val);
}
return to_string(sum);
}
//Method to check if arg is integer or string
// ret: True if int
bool isNumber(string x) {
regex e("^-?\\d+");
if (regex_match(x, e)) return true;
else return false;
}
//Recursive call to evaluate the set of expressions
string evaluate_eq(string key)
{
string expr, var;
vector<string> items;
vector<string>::iterator i;
auto temp = mymap.find(key);
if (temp != mymap.end()) // check temp is pointing to underneath element of a map
{
//fetch lhs
var = temp->first;
//fetch rhs
expr = temp->second;
}
// remove whitespaces
expr.erase(remove_if(expr.begin(), expr.end(), isspace), expr.end());
//Parse RHS by '+' sign
items = parse_expr(expr, "+");
for (i = items.begin(); i != items.end(); i++)
{
//cout << (*i) << endl;
if (isNumber(*i) == true)
{
//pass- do nothiing
}
else
{
//recursive call to evaluate unknown
string c = evaluate_eq(*i);
//now update the map and Find Sum vector
mymap[key] = c;
*i = c;
}
}
//find sum
return find_VctrSum(key, items);
}
//main to parse input from text file and evaluate
int main()
{
string line;
ifstream myfile("equation.txt");
vector<string> v;
if (myfile.is_open())
{
while (getline(myfile, line))
{
v.push_back(line);
}
myfile.close();
}
else cout << "Unable to open file";
//Create a map with key:variable and value: expression to solve
for (int i = 0; i < v.size(); i++)
{
vector<string> token;
token = parse_expr(v[i], "=");
mymap.insert(pair<string, string>(token[0], token[1]));
}
cout << "Equation sets given:" << endl;
for (map<string, string>::iterator it = mymap.begin(); it != mymap.end(); ++it)
{
std::cout << it->first << " => " << it->second << '\n';
}
for (map<string, string>::iterator it = mymap.begin(); it != mymap.end(); it++)
{
//Also update the map
mymap[it->first] = evaluate_eq(it->first);
}
cout << "Equation sets solved:" << endl;
for (map<string, string>::iterator it = mymap.begin(); it != mymap.end(); ++it)
{
std::cout << it->first << " => " << it->second << '\n';
}
char ch;
cin >> ch;
}
Logic is to call recursively for any unknown (string) if found while resolving a given expression and update the map with values. On debugging, I could see that my recursive call fails at below, but I see "mymap" is being updated. Not sure why.
if (temp != mymap.end())
Any help in identifying the issue or any logical lapse would be much appreciated.
Thanks

Answer 1

After fixing couple of logic, my code works correctly.
In main()
While, creating the input map create by striping whitespace
//Create a map with key:variable and value: expression to solve
for (int i = 0; i < v.size(); i++)
{
vector<string> token;
token = parse_expr(v[i], "=");
//Strip whitespaces
token[0].erase(remove_if(token[0].begin(), token[0].end(), isspace), token[0].end());
token[1].erase(remove_if(token[1].begin(), token[1].end(), isspace), token[1].end());
mymap.insert(pair<string, string>(token[0], token[1]));
}
This eliminate my issue of finding key in the map -
if (temp != mymap.end())
Updated my find_VctrSum to update the map here, unlike my earlier attempt to update in evaluate_eq().
//Method to find sum for a given vector
//retype: string
//ret: sum of given vector
string find_VctrSum(string key, vector<string> v)
{
int sum = 0;
string val;
vector<string>::iterator i;
for (i = v.begin(); i != v.end(); i++)
{
val = *i;
sum += stoi(val);
}
//Update the Map
mymap[key] = to_string(sum);
return to_string(sum);
}
Here is the complete working code -
#include <vector>
#include <string>
#include <sstream>
#include <iostream>
#include <map>
#include <fstream>
#include <set>
#include <regex>
using namespace std;
map<string, string> mymap;
// Method to Parse a given expression based on given arg delimiter
// ret: vector of parsed expression
vector<string> parse_expr(string n, char *delims)
{
vector<string> v;
string cleanline;
char* char_line = (char*)n.c_str(); // Non-const cast required.
char* token = NULL;
char* context = NULL;
vector<string>::iterator it;
token = strtok_s(char_line, delims, &context);
while (token != NULL)
{
cleanline += token;
cleanline += ' ';
v.push_back(token);
token = strtok_s(NULL, delims, &context);
}
return v;
}
//Method to find sum for a given vector
//retype: string
//ret: sum of given vector
string find_VctrSum(string key, vector<string> v)
{
int sum = 0;
string val;
vector<string>::iterator i;
for (i = v.begin(); i != v.end(); i++)
{
val = *i;
sum += stoi(val);
}
//Update the Map
mymap[key] = to_string(sum);
return to_string(sum);
}
//Method to check if arg is integer or string
// ret: True if int
bool isNumber(string x) {
regex e("^-?\\d+");
if (regex_match(x, e)) return true;
else return false;
}
//Recursive call to evaluate the set of expressions
string evaluate_eq(string key)
{
string expr, var;
vector<string> items;
vector<string>::iterator i;
string currentkey = key;
auto temp = mymap.find(key);
if (temp != mymap.end()) // check temp is pointing to underneath element of a map
{
//fetch lhs
var = key;
//fetch rhs
expr = temp->second;
}
// remove whitespaces
expr.erase(remove_if(expr.begin(), expr.end(), isspace), expr.end());
//Parse RHS by '+' sign
items = parse_expr(expr, "+");
for (i = items.begin(); i != items.end(); i++)
{
if (isNumber(*i) == true)
{
//pass- do nothiing
}
else
{
//recursive call to evaluate unknown
string c = evaluate_eq(*i);
//update the temp vector
*i = c;
}
}
//find sum
return find_VctrSum(key, items);
}
//main to parse input from text file and evaluate
int main()
{
string line;
ifstream myfile("equation.txt");
vector<string> v;
if (myfile.is_open())
{
while (getline(myfile, line))
{
v.push_back(line);
}
myfile.close();
}
else cout << "Unable to open file";
//Create a map with key:variable and value: expression to solve
for (int i = 0; i < v.size(); i++)
{
vector<string> token;
token = parse_expr(v[i], "=");
//Strip whitespaces
token[0].erase(remove_if(token[0].begin(), token[0].end(), isspace), token[0].end());
token[1].erase(remove_if(token[1].begin(), token[1].end(), isspace), token[1].end());
mymap.insert(pair<string, string>(token[0], token[1]));
}
cout << "Equation sets given:" << endl;
for (map<string, string>::iterator it = mymap.begin(); it != mymap.end(); ++it)
{
std::cout << it->first << " => " << it->second << '\n';
}
for (map<string, string>::iterator it = mymap.begin(); it != mymap.end(); it++)
{
//Also update the map
mymap[it->first] = evaluate_eq(it->first);
}
cout << "Equation sets solved:" << endl;
for (map<string, string>::iterator it = mymap.begin(); it != mymap.end(); ++it)
{
std::cout << it->first << " => " << it->second << '\n';
}
char ch;
cin >> ch;
}