How to find reverse relations between jobs? - c++

Question

I've been trying to find reverse relations between jobs. To be more specific I will tell it with an example.
Suppose I have n jobs i.e {0,1,2,3,4,...n}. I also have relations between jobs. I know only successor jobs, i.e., 2 is followed by 4,5. 5 is followed by 7,8 etc. I have it in a text file. I want to obtaing precedence relations between jobs (what is the predecessor job of 5?).
Having text output would be great. I have some code but it does not work.
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
using namespace std;
#define TOTAL_ACTIVITY 123
void readFile();
void change ();
void writeFile ();
struct Activity {
int precedessor [3];
int successor [3];
int id;
};
Activity activityList[TOTAL_ACTIVITY];
void main() {
readFile();
change();
writeFile();
}
void readFile() {
ifstream myReadFile;
myReadFile.open("pre.txt");
if (!myReadFile) { //check whether the file can be opened
cerr << "Unable to open file"; // terminate with error
}
while (!myReadFile.eof()) {
int Id,suc1, suc2, suc3;
int t = 0;
while (myReadFile >> Id >> suc1 >> suc2 >> suc3) //data should be in this order
{
activityList[t].id = Id;
activityList[t].successor [0] = suc1;
activityList[t].successor [1] = suc2;
activityList[t].successor [2] = suc3;
t++;
}
}
return;
}
void change() {
int act;
for (int i=1;i<TOTAL_ACTIVITY;i++){
for (int j=0;j<TOTAL_ACTIVITY;j++){
for (int k=0;k<3;k++) {
if (activityList[j].successor[k]==i;)
}
}
}
}
void writeFile() {
ofstream out("out.txt");
out << "id\t" << "Pre1\t" << "Pre2\t" << "Pre3\t"<<"\n";
for (int j = 0; j < TOTAL_ACTIVITY; j++) {
out << activityList[j].id << "\t";
out << activityList[j].precedessor[0]<< "\t";
out << activityList[j].precedessor[1] << "\t";
out << activityList[j].precedessor[2] << "\t";
out << "\n";
}
out.close();
}
Here is a sample input:
ID Successor1 Successor2 Successor3
1 2 3 4
2 6 11 15
3 7 8 13
4 5 9 10
5 20
6 30
7 27
8 12 19 27
9 14
10 16 25
11 20 26
12 14
13 17 18
14 17
15 25
16 21 22
17 22
18 20 22
19 24 29
20 23 25
21 28
22 23
23 24
24 30
25 30
26 31
27 28
28 31
29 32
30 32
31 32
Output should be something like this:
Id Predecesor1 Predecesor2 Predecesor3
........................................
...........................................
...........................................

Answer 1

You are given the successors of a job, but you do not need to retain this information.
For example, if I say: 5 -> 6, 7 meaning that 5 is followed by 6 and 7, then it is equivalent to saying that 6 and 7 are preceded by 5, right.
You can then either:
directly output the precedence when reading the successors
store in an associative container, using the job id as the key and the predecessor as value
Specifics details... are for you to work out to conclude your homework.