我几乎完成了编码以解决简单的线性方程组。似乎在地图导致问题的递归调用中遗漏了一些东西。
这是要解决的问题陈述，例如：
X = Y + 2
Y = Z + R + 1
R = 2 + 3
Z = 1
鉴于：LHS只是变量名称。 RHS只有变量，unsigned int和'+'运算符。解决所有未知因素。
我的代码解决方案：
X = 2
Y = 1
R = 5
Z = 1
我的代码：
#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;
//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;
}
逻辑是在解析给定表达式时使用任何未知（字符串）递归调用，并使用值更新映射。在调试时，我可以看到我的递归调用在下面失败，但我看到“mymap”正在更新。不知道为什么。
if (temp != mymap.end())
任何帮助确定问题或任何合理的失误都将非常感激。 感谢
答案 0 :(得分：0)
修复几个逻辑后，我的代码工作正常。
同时，通过条带化空白创建输入映射
//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]));
}
这消除了我在地图中找到密钥的问题 -
if (temp != mymap.end())
//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;
}