interview solution

solution.cpp

#include <vector>
#include <map>
#include <string>
#include <iostream>
#include <cctype>

using namespace std;

bool Substitude(const string &template_str, map<string,string> &mapping, string &output) {
    int state=0;
    string var;
    for(auto &c:template_str) {
        switch(c) {
            case '$':
                if(state == 0) {
                    state=1;
                } else if(state == 1) {
                    if(var.empty()) {
                        output+=c;
                        state=0;
                    } else {
                        auto r=mapping.find(var);
                        if(r != mapping.end())
                            output+=r->second;
                        else
                            return false;
                        state=1;
                        var.clear();
                    }

                } else {
                    var+=c;
                }
                break;
            case '{':
                if(state == 0)
                    output+=c;
                else if(state == 1)
                    state=2;
                else
                    var+=c;
                break;
            case '}':
                if(state == 0)
                    output+=c;
                else if(state == 1)
                    var+=c;
                else {
                    auto r=mapping.find(var);
                    if(r != mapping.end())
                        output+=r->second;
                    else
                        return false;
                }
                state=0;
                var.clear();
                break;
            default:
                if(state == 0)
                    output+=c;
                else if(state == 1) {
                    if(isalnum(c)) {
                        var+=c;
                    } else {
                        auto r=mapping.find(var);
                        if(r != mapping.end())
                            output+=r->second;
                        else
                            return false;
                        output+=c;
                        state=0;
                        var.clear();
                    }
                }
                else
                    var+=c;

        }
    }
    if(state == 0)
        return true;
    else if(state == 1) {
        auto r=mapping.find(var);
        if(r != mapping.end())
            output+=r->second;
        else
            return false;
        return true;
    }
    else
        return false;
}

int main() {
    string template_str("abc$$def$VAR1-${VAR2}def");
    map<string,string> mapping;
    mapping.emplace(make_pair(string("VAR1"),string("ricky")));
    mapping.emplace(make_pair(string("VAR2"),string("zhang")));
    string output;
    if(Substitude(template_str,mapping,output))
        cout<<"the result:"<<output<<endl;
    else
        cout<<"something goes wrong"<<endl;
}