CS50 – Week 3 – Runoff

OK, so runoff seems much easier than Tideman which is so far a fail for me. I did find a few things –

• If you want to do Tideman, it’s best to do Runoff first to get your brain thinking in this fashion.
• How the course instructions are set up to use the arrays and index into the arrays can be difficult to wrap your head around. Paper and pen help. And debug50!
• I lost quite a lot of time with errors in coding, certain logic steps incorrect, or making errors like returning the same true/false in both places in a function when true was needed in 1 decision, and false in the other. Perhaps tired or just trying to rush or whatever. Anyway, took longer than it should of.
• The basics of using code are relatively easy – A lot of for loops, indexing into arrays (read/write), and basic decision points. It’s the use of data structures and general flow of the program that takes time to understand.

Here’s some of the code.

#include <cs50.h>
#include <stdio.h>
#include <string.h>

// Max voters and candidates
#define MAX_VOTERS 100
#define MAX_CANDIDATES 9

// preferences[i][j] is jth preference for voter i
int preferences[MAX_VOTERS][MAX_CANDIDATES];

// Candidates have name, vote count, eliminated status
typedef struct
{
    string name;
    int votes;
    bool eliminated;
}
candidate;

// Array of candidates
candidate candidates[MAX_CANDIDATES];

// Numbers of voters and candidates
int voter_count;
int candidate_count;

// Function prototypes
bool vote(int voter, int rank, string name);
void tabulate(void);
bool print_winner(void);
int find_min(void);
bool is_tie(int min);
void eliminate(int min);

int main(int argc, string argv[])
{
    // Check for invalid usage
    if (argc < 2)
    {
        printf("Usage: runoff [candidate ...]\n");
        return 1;
    }

    // Populate array of candidates
    candidate_count = argc - 1;
    if (candidate_count > MAX_CANDIDATES)
    {
        printf("Maximum number of candidates is %i\n", MAX_CANDIDATES);
        return 2;
    }
    for (int i = 0; i < candidate_count; i++)
    {
        candidates[i].name = argv[i + 1];
        candidates[i].votes = 0;
        candidates[i].eliminated = false;
    }

    voter_count = get_int("Number of voters: ");
    if (voter_count > MAX_VOTERS || voter_count < 1)
    {
        printf("Maximum number of voters is %i, minimum is 1\n", MAX_VOTERS);
        return 3;
    }

    // Keep querying for votes - runs for EACH VOTER

    for (int i = 0; i < voter_count; i++)
    {

        // Query for each rank - GET THE FULL RANK LIST CANDIDATES FROM THAT VOTER
        for (int j = 0; j < candidate_count; j++)
        {
            string name = get_string("Rank %i: ", j + 1);

            // Record vote, unless it's invalid - CALLED ONCE PER CANDIDATE RANK ENTRY
            // i = voter
            // j = candidate rank
            if (!vote(i, j, name))
            {
                printf("Invalid vote.\n");
                return 4;
            }
        }

        printf("\n");
    }

    // Keep holding runoffs until winner exists
    while (true)
    {
        // Calculate votes given remaining candidates
        tabulate();

        printf("out of tabulate\n");

        // Check if election has been won
        bool won = print_winner();
        if (won)
        {
            break;
        }

        // Eliminate last-place candidates
        int min = find_min();
        bool tie = is_tie(min);

        // If tie, everyone wins
        if (tie)
        {
            for (int i = 0; i < candidate_count; i++)
            {
                if (!candidates[i].eliminated)
                {
                    printf("%s\n", candidates[i].name);
                }
            }
            break;
        }

        // Eliminate anyone with minimum number of votes
        eliminate(min);

        // Reset vote counts back to zero
        for (int i = 0; i < candidate_count; i++)
        {
            candidates[i].votes = 0;
        }
    }
    return 0;
}

// Record preference if vote is valid
bool vote(int voter, int rank, string name)
{
    for (int i = 0; i < candidate_count; i++)
    {
        if (!strcmp(name, candidates[i].name))
        {
            // preferences has voter as the rows
            // preferences has the preferences - ie the ranks as the columns
            // find the matching name, if exists. --> and put the INDEX of the candidate FOUND / MATCHED at that spot

           return true;
        }
    }
    return false;
}

// Tabulate votes for non-eliminated candidates
// meant to iterate over all candidates!
void tabulate(void)
{
    for (int v = 0; v < voter_count; v++)
    {
        for (int pref = 0; pref < candidate_count; pref++)
        {
         
        }
    }
    return;
}

// Print the winner of the election, if there is one
bool print_winner(void)
{
    for (int pref = 0; pref < candidate_count; pref++)
    {
        if (candidates[pref].votes > (voter_count / 2))
        {
            printf("%s\n", candidates[pref].name);
            return true;
        }
    }
    printf("Did not find winner\n");
    return false;
}

// Return the minimum number of votes any remaining candidate has
int find_min(void)
{
    int min_vote = voter_count; // set high to start with
    
    return min_vote;
}

// Return true if the election is tied between all candidates, false otherwise
bool is_tie(int min)
{

    for (int pref = 0; pref < candidate_count; pref++)
    {
       
    }
    return true;
}

// Eliminate the candidate (or candidates) in last place
void eliminate(int min)
{
    printf("in eliminate\n");
    for (int pref = 0; pref < candidate_count; pref++)
    {
        
    }
    return;
}