[英]Issue with implementing recursive function for finding paths
我正在嘗試打印從A站到L站的地鐵系統中的所有可能路徑。換句話說,目標是找到一個人可以通過多少條路線來通過地鐵系統而無需越過軌道不止一次。 我知道有640條可能的路徑,因為我之前在C中使用鄰接矩陣編寫了此程序。 現在,我嘗試編寫相同的程序,除了在C ++中使用類而不使用鄰接矩陣。
我遇到的問題是我似乎無法正確實現我的遞歸函數SearchRoute,因為我需要打印路徑,標記路徑,然后再次取消標記路徑以允許回溯。 當我打印出最終結果時,我只會看到從A到B的音軌,這顯然意味着有些錯誤。
這就是我認為的問題:我知道在SubwaySystem :: SearchRoute函數中使用了if and else語句,該語句顯然不允許調用遞歸函數,但是我嘗試放置另一個if語句而不是else,但是我我不太確定情況會怎樣。
void SubwaySystem::SearchRoute(int Current_Station_ID)
{
while(Current_Station_ID < 33)
{
cout << "In while loop\n";
// \\ Checking progress
if(Current_Station_ID == 0) //Find a successful route to Station L
{
count_routes++; //Add 1 into the variable “count_routes”
cout << "In if statement\n";
// \\Checking progress
cout << count_routes << " " << my_track[Current_Station_ID] << endl; //Print out this route
return;
}
else //Get into recursive Function Body
{
for(int i = my_station[Current_Station_ID].track_starting_ID; i < my_station[Current_Station_ID].track_starting_ID + my_station[Current_Station_ID].track_size; i++)
{
if(my_track[Current_Station_ID].visited == 0) //if this track is not visited before
{
cout << "In recursive part of function\n";
// \\ Checking progress
my_track[Current_Station_ID].visited = 1; //mark this track as visited
my_track[Current_Station_ID].node_2 = 1; //mark its corresponding track as visited
cout << my_track[Current_Station_ID] << endl; //save this track
SearchRoute(Current_Station_ID + 1); //Recursive
i--; //Backtrack this track
my_track[Current_Station_ID].visited = 0;//mark this track as unvisited
my_track[Current_Station_ID].node_2 = 0;//mark its corresponding track as unvisited
}
}
}
}
}
我也嘗試在打印語句的過程中跟蹤整個程序的進度。 由於上面指定的原因,我的遞歸函數從未被調用(至少這就是為什么我認為它不起作用的原因)。 由於某種原因,我無法弄清楚為什么多次調用默認和重載軌道構造函數的原因。
如果您能幫助我找出代碼中的問題區域/向我展示正確的方法,將不勝感激。 我厭倦了對此的思考。 提前致謝。
這是單個TU中程序的其余部分:
//Function Declarations
#include <iostream>
#include <string>
using namespace std;
#ifndef SUBWAY_H
#define SUBWAY_H
class Track
{
public:
//Default Constructor
Track();
//Overload Constructor
Track(char, char);
//Destructor
~Track();
//Member variables
char node_1;
char node_2;
bool visited;
};
class Station
{
public:
//Default Constructor
Station();
//Destructor
~Station();
//Overload Constructor
Station(char, int, int);
//Member variables
char station_name;
int track_starting_ID;
int track_size;
};
class SubwaySystem
{
public:
//Default Constructor
SubwaySystem();
//Destructor
~SubwaySystem();
//Recursive function
void SearchRoute(int);
//Other member functions
friend ostream& operator<<(ostream& os, const Track& my_track);
friend ostream& operator<<(ostream& os, const Station& my_station);
//Member variables
Track my_track[34];
Station my_station[12];
int count_routes;
int Current_Station_ID;
//String to save found route
};
#endif
// **cpp**
//Function Definitions
#include <iostream>
#include <string>
//#include "subway.h"
using namespace std;
Track::Track()
{
visited = 0;
//cout << "Default Track has been called\n";
//\\ Checking progress
}
Track::~Track()
{
}
Track::Track(char pass_track1, char pass_track2)
{
node_1 = pass_track1;
node_2 = pass_track2;
visited = false;
//cout << "Overload Track constructor has been called\n";
// \\ Checking progress
}
Station::Station()
{
}
Station::~Station()
{
}
Station::Station(char pass_station_name, int pass_start, int pass_size)
{
station_name = pass_station_name;
track_starting_ID = pass_start;
track_size = pass_size;
//cout << "Overload station has been called\n";
// \\ Checking progress
}
SubwaySystem::SubwaySystem()
{
//Initialize tracks
//node_1, node_2
my_track[0] = Track('a', 'b');
my_track[1] = Track('b', 'a');
my_track[2] = Track('b', 'c');
my_track[3] = Track('b', 'd');
my_track[4] = Track('b', 'e');
my_track[5] = Track('b', 'f');
my_track[6] = Track('c', 'b');
my_track[7] = Track('c', 'e');
my_track[8] = Track('d', 'b');
my_track[9] = Track('d', 'e');
my_track[10] = Track('e', 'b');
my_track[11] = Track('e', 'c');
my_track[12] = Track('e', 'd');
my_track[13] = Track('e', 'g');
my_track[14] = Track('e', 'h');
my_track[15] = Track('f', 'b');
my_track[16] = Track('f', 'h');
my_track[17] = Track('g', 'e');
my_track[18] = Track('g', 'k');
my_track[19] = Track('h', 'e');
my_track[20] = Track('h', 'f');
my_track[21] = Track('h', 'i');
my_track[22] = Track('h', 'j');
my_track[23] = Track('h', 'k');
my_track[24] = Track('i', 'h');
my_track[25] = Track('i', 'k');
my_track[26] = Track('j', 'h');
my_track[27] = Track('j', 'k');
my_track[28] = Track('k', 'g');
my_track[29] = Track('k', 'h');
my_track[30] = Track('k', 'i');
my_track[31] = Track('k', 'j');
my_track[32] = Track('k', 'l');
my_track[33] = Track('l', 'k');
//Initialize stations
//station_name, track_starting_ID, track_size
my_station[0] = Station('a', 0, 1);
my_station[1] = Station('b', 1, 5);
my_station[2] = Station('c', 6, 2);
my_station[3] = Station('d', 8, 2);
my_station[4] = Station('e', 10, 5);
my_station[5] = Station('f', 15, 2);
my_station[6] = Station('g', 17, 2);
my_station[7] = Station('h', 19, 5);
my_station[8] = Station('i', 24, 2);
my_station[9] = Station('j', 26, 2);
my_station[10] = Station('k', 28, 5);
my_station[11] = Station('l', 33, 1);
//Initiaize other members
count_routes = 0;
Current_Station_ID = 0;
//cout << "SubwaySystem constructor called\n";
// \\ Checking progress
}
SubwaySystem::~SubwaySystem()
{
}
ostream& operator<<(ostream& os, const Track& my_track)
{
os << my_track.node_1 << '.' << my_track.node_2;
return os;
}
ostream& operator<<(ostream& os, const Station& my_station)
{
os << my_station.station_name << '.' << my_station.track_starting_ID << '.' << my_station.track_size;
return os;
}
//This is where the above recursive function SearchRoute goes. I posted it separately so it's easier to read.
// **main**
#include <iostream>
#include <string>
//#include "subway.h"
using namespace std;
int main(int argc, char **argv)
{
SubwaySystem Test;
Test.SearchRoute(0);
}
很抱歉,如果“檢查進度”打印語句使閱讀代碼更加困難。
您永遠不會輸入遞歸:
// this method is called with value 0
void SubwaySystem::SearchRoute(int Current_Station_ID)
{
while(Current_Station_ID < 33)
{
cout << "In while loop\n";
// \\ Checking progress
if(Current_Station_ID == 0) //Find a successful route to Station L
{
count_routes++; //Add 1 into the variable “count_routes”
cout << "In if statement\n";
// \\Checking progress
cout << count_routes << " " << my_track[Current_Station_ID] << endl; //Print out this route
return; // ERROR: here you return from the very 1st method call, breaking the search
}
基本上,不用為您編寫代碼,我建議這樣做:
遞歸函數根本不應該包含while語句(遞歸函數的全部要點在於它本身就是一個while語句)。
遞歸函數中的第一件事應該是檢查站ID是否緊鄰“ L”站,或者是否已經采用了唯一的路徑。 如果相鄰,則可以返回從該電台到L的音軌。
如果沒有,則為所有尚未到達您的路徑的相鄰站點調用遞歸函數,並將它們的結果用作當時所在站點的計算的一部分。
要根據您的數據舉例說明:
這樣可以澄清事情嗎?
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