用映射求解线性方程

//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);
}

这是完整的工作代码-

#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;
}