I've been stuck on this function of the PSET for a couple of days now. I have met every requirement in check50 except for the one that says, ":( lock_pairs skips final pair if it creates a cycle; lock_pairs did not correctly lock all non-cyclical pairs"
Here is my code:
#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <stdbool.h>
// Max number of candidates
#define MAX 9
// preferences[i][j] is number of voters who prefer i over j
int preferences[MAX][MAX];
// locked[i][j] means i is locked in over j
bool locked[MAX][MAX];
// Each pair has a winner, loser
typedef struct
{
int winner;
int loser;
}
pair;
// Array of candidates
string candidates[MAX];
pair pairs[MAX * (MAX - 1) / 2];
int pair_count;
int candidate_count;
// Function prototypes
bool vote(int rank, string name, int ranks[]);
void record_preferences(int ranks[]);
void add_pairs(void);
void sort_pairs(void);
void lock_pairs(void);
void print_winner(void);
bool makes_cycle(int x, int y);
bool makes_cycle2(int tmp, int y);
int main(int argc, string argv[])
{
// Check for invalid usage
if (argc < 2)
{
printf("Usage: tideman [candidate ...]\n");
return 1;
}
// Populate array of candidates
candidate_count = argc - 1;
if (candidate_count > MAX)
{
printf("Maximum number of candidates is %i\n", MAX);
return 2;
}
for (int i = 0; i < candidate_count; i++)
{
candidates[i] = argv[i + 1];
}
// Clear graph of locked in pairs
for (int i = 0; i < candidate_count; i++)
{
for (int j = 0; j < candidate_count; j++)
{
locked[i][j] = false;
}
}
pair_count = 0;
int voter_count = get_int("Number of voters: ");
// Query for votes
for (int i = 0; i < voter_count; i++)
{
// ranks[i] is voter's ith preference
int ranks[candidate_count];
// Query for each rank
for (int j = 0; j < candidate_count; j++)
{
string name = get_string("Rank %i: ", j + 1);
if (!vote(j, name, ranks))
{
printf("Invalid vote.\n");
return 3;
}
}
record_preferences(ranks);
printf("\n");
}
add_pairs();
sort_pairs();
lock_pairs();
print_winner();
return 0;
}
// Update ranks given a new vote
bool vote(int rank, string name, int ranks[])
{
// For every candidate
for (int i = 0; i < candidate_count; i++)
{
// Check if the name matches the candidates name ignoring case
if (strcasecmp(name, candidates[i]) == 0)
{
// Store the index of that name into the user's "rank"th ranks array and return true
ranks[rank] = i;
return true;
}
}
return false;
}
// Update preferences given one voter's ranks
void record_preferences(int ranks[])
{
// Loop through everybody in the voter's ranks
for (int i = 0; i < candidate_count; i++)
{
// For every person after the person we're looking at in the voter's rank
for (int j = i + 1; j < candidate_count; j++)
{
// Update preferences array
preferences[ranks[i]][ranks[j]]++;
}
}
return;
}
// Record pairs of candidates where one is preferred over the other
void add_pairs(void)
{
// Initialize variable "position" to keep track of position in pairs array
int position = 0;
// For every votable candidate
for (int i = 0; i < candidate_count; i++)
{
// For every votable candidate
for (int j = 0; j < candidate_count; j++)
{
// If the people who prefer candidate[i] over candidate[j] is not 0
if (preferences[i][j] > 0 && preferences[i][j] > preferences[j][i])
{
// Increment pair_count
pair_count++;
// Add the pair to the pairs array at index "position"
pairs[position].winner = i;
pairs[position].loser = j;
// Increment positions for the next pair
position++;
}
}
}
return;
}
// Sort pairs in decreasing order by strength of victory
void sort_pairs(void)
{
// Initialize a buffer pair struct
pair temp;
// Initialize variable to store value for selection sort
int most = 0;
// For every pair, organize the array by descending strength of victory
for (int i = 0; i < pair_count; i++)
{
// For every pair, figure out largest strength of victory and store that in the firstmost index of the array
for (int j = i; j < pair_count; j++)
{
// Access the winner and loser values as coordinates in the 2d preferences array
int x = pairs[j].winner;
int y = pairs[j].loser;
// Find the strength of the candidate's victory
int diff = preferences[x][y] - preferences[y][x];
// If strength of victory is greatest yet, switch values of the firstmost index with current index
if (diff > most)
{
most = diff;
temp.winner = pairs[i].winner;
temp.loser = pairs[i].loser;
pairs[i].winner = pairs[j].winner;
pairs[i].loser = pairs[j].loser;
pairs[j].winner = temp.winner;
pairs[j].loser = temp.loser;
}
}
}
return;
}
// Lock pairs into the candidate graph in order, without creating cycles
void lock_pairs(void)
{
// Initialize every value to false in locked_pairs
for (int i = 0; i < candidate_count; i++)
{
for (int j = 0; j < candidate_count; j++)
{
locked[i][j] = false;
}
}
// For every pair
for (int i = 0; i < pair_count; i++)
{
// Initialize variables to the winner and loser values in pairs
int x = pairs[i].winner;
int y = pairs[i].loser;
// If locking an edge does not create a cycle
if (makes_cycle(x, y) == false)
{
// Lock in the edge
locked[x][y] = true;
}
}
return;
}
// Print the winner of the election
void print_winner(void)
{
// Search for the source of the graph by finding a person over whom nobody has an edge
// For every candidate (horizontal on 2d locked array)
for (int i = 0; i < candidate_count; i++)
{
// For every candidate (vertical on 2d locked array)
for (int j = 0; j < candidate_count; j++)
{
// If nothing in the horizontal array of that candidate is true
if (locked[j][i] == true)
{
break;
}
else if (locked[j][i] == false && j == candidate_count - 1)
{
printf("%s\n", candidates[i]);
return;
}
}
}
return;
}
// If locking in an edge makes a cycle return false; otherwise return true
bool makes_cycle(int x, int y)
{
// Store the value of y in a temp variable for now
int tmp = x;
bool makes_cycle = makes_cycle2(tmp, y);
if (makes_cycle)
{
return true;
}
return false;
}
bool makes_cycle2(int tmp, int y)
{
// If, when inserted into the x column, the value of y points to something, go to it and see if it leads to y
// For every candidate
for (int i = 0; i < candidate_count; i++)
{
// If, when inserted into the x column, the value of y points to something
if (locked[y][i] == true)
{
// Set y equal to that value
y = i;
// Check again until the value of y in the x column never edges over anything
if (y == tmp)
{
return true;
}
// Call the function again FIGURE OUT POSITION THING
makes_cycle2(tmp, y);
}
}
return false;
}
I know the variable names are vague and there are several inefficiencies, but trying to fix these just led to more issues than before, so I just undid a couple hours of work to get back to the inefficient but more complete code. Could someone please explain why I am able to lock in a middle value correctly but not a final value? Thank you in advance for any advice you give me!
PS: I have asked this question in the discord server and someone said that where I changed the y variable in makes_cycle2() was where I was going wrong since my if condition would be messed up if I did that. If someone could explain what that means in addition to giving feedback on my code, it would be greatly appreciated! I hope you have a great day!
