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| #include <cs50.h>
#include <stdio.h>
#include <string.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 is_circle(int start_winner, int loser);
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 (int k = 0; k < candidate_count; k++)
{
if (strcmp(candidates[k], name) == 0)
{
ranks[rank] = k;
return true;
}
}
return false;
}
// Update preferences given one voter's ranks
void record_preferences(int ranks[])
{
for (int j = 0; j < candidate_count; j++)
{
for (int k = 0; k < (candidate_count - j); k++)
{
preferences[ranks[j]][ranks[ j + k + 1]]++;
}
}
return;
}
// Record pairs of candidates where one is preferred over the other
void add_pairs(void)
{
for (int i = 0; i < candidate_count; i++)
{
for (int j = 0; j < candidate_count; j++)
{
if (i != j)
{
if (preferences[i][j] > preferences[j][i])
{
pairs[pair_count].winner = i;
pairs[pair_count].loser = j;
pair_count++;
}
}
}
}
return;
}
// Sort pairs in decreasing order by strength of victory
void sort_pairs(void)
{
for (int i = 0; i < pair_count; i++)
{
for (int j = i + 1; j < pair_count; j++)
{
if ((preferences[pairs[i].winner][pairs[i].loser]) < (preferences[pairs[j].winner][pairs[j].loser]))
{
pair temp_pair;
temp_pair.winner = pairs[i].winner;
temp_pair.loser = pairs[i].loser;
pairs[i].winner = pairs[j].winner;
pairs[i].loser = pairs[j].loser;
pairs[j].winner = temp_pair.winner;
pairs[j].loser = temp_pair.loser;
}
}
}
return;
}
// Lock pairs into the candidate graph in order, without creating cycles
void lock_pairs(void)
{
for (int i = 0; i < pair_count; i++)
{
if (!is_circle(pairs[i].winner, pairs[i].loser))
{
locked[pairs[i].winner][pairs[i].loser] = true;
}
}
return;
}
// Print the winner of the election
void print_winner(void)
{
int winner = -1;
for (int i = 0; i < candidate_count; i++)
{
for (int j = 0; j < candidate_count; j++)
{
if (winner == -1 && locked[i][j])
{
winner = i;
}
if (locked[i][j] && j == winner)
{
winner = i;
}
}
}
printf("%s\n", candidates[winner]);
return;
}
bool is_circle(int start_winner, int loser)
{
if (loser == start_winner)
{
return true;
}
for (int i = 0; i < candidate_count; i++)
{
if (locked[loser][i])
{
if (is_circle(start_winner, i))
{
return true;
}
}
}
return false;
}
|
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