I worked with pset3 and I think there are nothing wrong with my code, but check 50 says it has 2 problems on my code.
1.:( lock_pairs skips final pair if it creates cycle
2.:( lock_pairs skips middle pair if it creates a cycle
All examples which I can imagine could pass the test with this code... This is my sorting part:
// Lock pairs into the candidate graph in order, without creating cycles
void lock_pairs(void)
{
// TODO
for(int i =0;i<pair_count;i++)
{
locked[pairs[i].winner][pairs[i].loser]=true;
int cycle=0;
for(int w=0;w<candidate_count;w++)
{
int false_count=0;
for(int l=0;l<candidate_count;l++)
{
if(locked[l][w]==false)
{
false_count++;
}
}
if(false_count==candidate_count)
{
cycle ++;
printf("cycle %i\n",cycle);
}
}
if(cycle==0)
{
locked[pairs[i].winner][pairs[i].loser]=false;
}
}
return;
}
and here is my code. Can you explain why my code is not correct?
#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);
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[])
{
// TODO
for(int i = 0;i < candidate_count;i++)
if(strcmp(candidates[i],name)==0)
{
ranks[rank]=i;
return true;
}
return false;
}
// Update preferences given one voter's ranks
void record_preferences(int ranks[])
{
// TODO
for(int i=0;i<candidate_count-1;i++)
{
for(int j=1;i+j<candidate_count;j++)
{
preferences[ranks[i]][ranks[i+j]]++;
}
}
return;
}
// Record pairs of candidates where one is preferred over the other
void add_pairs(void)
{
// TODO
for(int i=0;i<candidate_count-1;i++)
{
for(int j=1;i+j<candidate_count;j++)
{
if(preferences[i][i+j]>preferences[i+j][i])
{
pairs[pair_count].winner=i;
pairs[pair_count].loser=i+j;
pair_count++;
}
else if(preferences[i][i+j]<preferences[i+j][i])
{
pairs[pair_count].winner=i+j;
pairs[pair_count].loser=i;
pair_count++;
}
}
}
return;
}
// Sort pairs in decreasing order by strength of victory
void sort_pairs(void)
{
// TODO
for(int r=0;r<pair_count;r++)
{
int i=0;
int z=0;
for(int j=0;j<pair_count;j++)
{
if(preferences[pairs[j+r].winner][pairs[j+r].loser]>i)
{
i=preferences[pairs[j+r].winner][pairs[j+r].loser];
}
}
for(int y=0;y<pair_count;y++)
{
if(preferences[pairs[y+r].winner][pairs[y+r].loser]==i)
{
z =y+r;
}
}
int w=pairs[r].winner;
int l=pairs[r].loser;
pairs[r].winner=pairs[z].winner;
pairs[r].loser=pairs[z].loser;
pairs[z].winner=w;
pairs[z].loser=l;
}
}
// Lock pairs into the candidate graph in order, without creating cycles
void lock_pairs(void)
{
// TODO
for(int i =0;i<pair_count;i++)
{
locked[pairs[i].winner][pairs[i].loser]=true;
int cycle=0;
for(int w=0;w<candidate_count;w++)
{
int false_count=0;
for(int l=0;l<candidate_count;l++)
{
if(locked[l][w]==false)
{
false_count++;
}
}
if(false_count==candidate_count)
{
cycle ++;
printf("cycle %i\n",cycle);
}
}
if(cycle==0)
{
locked[pairs[i].winner][pairs[i].loser]=false;
}
}
return;
}
// Print the winner of the election
void print_winner(void)
{
// TODO
int l=0;
int w=0;
while(w!=candidate_count&&l!=candidate_count)
{
if(locked[w][l]==true)
{
w=0;
l++;
}
else//if(locked[w][l]=false)
{
if(w==candidate_count-1)
{
printf("%s\n",candidates[l]);
}
w++;
}
}
return;
}
Thank you!!
