[Week 3] Algorithms

과제

Sort

sort1 uses: Bubble Sort

How do you know?: Takes slightly less amount of time when running on sorted texts compared to sort3

sort2 uses: Merge Sort

How do you know?: Is the fastest among all.

sort3 uses: Selection Sort

How do you know?: Takes lot of time even when running on sorted text compared to sort1

 

pluarity

 

 

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

// Max number of candidates
#define MAX 9

// Candidates have name and vote count
typedef struct
{
    string name;
    int votes;
}
candidate;

// Array of candidates
candidate candidates[MAX];

// Number of candidates
int candidate_count;

// Function prototypes
bool vote(string name);
void print_winner(void);

int main(int argc, string argv[])
{
    // Check for invalid usage
    if (argc < 2)
    {
        printf("Usage: plurality [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].name = argv[i + 1];
        candidates[i].votes = 0;
    }

    int voter_count = get_int("Number of voters: ");

    // Loop over all voters
    for (int i = 0; i < voter_count; i++)
    {
        string name = get_string("Vote: ");

        // Check for invalid vote
        if (!vote(name))
        {
            printf("Invalid vote.\n");
        }
    }

    // Display winner of election
    print_winner();
}

// Update vote totals given a new vote
bool vote(string name)
{
    //Loop through the Candidate count
    for (int i = 0; i < candidate_count; i++)
    {
        //check if candidate is similar to what is user's vote
        if (strcmp(candidates[i].name, name) == 0)
        {
            //if similar to what user vote for, then increase the specific candidate vote and return true
            candidates[i].votes++;
            return true;
        }
    }
    //else if not similar to candidate vote return false.....and print invalid vote
    return false;
}

// Print the winner (or winners) of the election
void print_winner(void)
{
    //Create and variable and set it to 0
    int maximum_vote = 0;

    //iterate over list of candidate
    for (int i = 0; i < candidate_count; i++)
    {
        //check for candidate votes that are  greater than maximum_vote and set them to maximum_vote
        if (candidates[i].votes > maximum_vote)
        {
            maximum_vote = candidates[i].votes;
        }
    }

    //iterate over list of candidate
    for (int i = 0; i < candidate_count; i++)
    {
        //check for candidate votes that are equal to maximum vote and print them as you go
        if (candidates[i].votes == maximum_vote)
        {
            printf("%s\n", candidates[i].name);
        }
    }

    return;
}

 

 

runoff

문제 바로가기

Runoff - CS50x 2021

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

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

// preferences[i][j] is jth preference for voter i(2d array)
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)
    {
        printf("Maximum number of voters is %i\n", MAX_VOTERS);
        return 3;
    }

    // Keep querying for votes
    for (int i = 0; i < voter_count; i++)
    {

        // Query for each rank
        for (int j = 0; j < candidate_count; j++)
        {
            string name = get_string("Rank %i: ", j + 1);

            // Record vote, unless it's invalid
            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();

        // 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
//passed i,j and name of the candidate the user entered, look at line 77
bool vote(int voter, int rank, string name)
{
    bool exist = false;
    for (int i = 0; i < candidate_count; i++)
    {
        //check if name is present in the candidates entered by the user by camparing two strings 
        //strcmp is checking for the name and camparing it to the candidates array location 'i' which starts according to the for loop above 
        if (strcmp(name, candidates[i].name) == 0)
        {
            //if you found the person is present then add that number as a rank of the candidate in the preferences array
            //suppose this is a 2d array and the preference array is adding the preference number on a specific poistion so 
            // here ex - preferences[0][0] = i (the rank preferences from the candidate count) 
            // [i][][][]
            // [][][][]
            // [][][][]
            // [][][][]
            preferences[voter][rank] = i;
            exist = true;
            break;
            //This is a bool conditions which will become true, again look at line 77 
        }
    }
    return exist;
}

// Tabulate votes for non-eliminated candidates
void tabulate(void)
{
    // TODO
    for (int i = 0; i < voter_count; i++)
    {
        for (int j = 0; j < candidate_count; j++)
        {
            if (candidates[preferences[i][j]].eliminated == false)
            {
                candidates[preferences[i][j]].votes += 1;
                break;
            }
        }
        
    }

    return;
}

// Print the winner of the election, if there is one
bool print_winner(void)
{
    // TODO
    for (int i = 0; i < candidate_count; i++)
    {
        string most = candidates[i].name;
        if (candidates[i].votes > voter_count / 2)
        {
            printf("%s\n", most);
            return true;
        }
    }
    return false;
}

// Return the minimum number of votes any remaining candidate has
int find_min(void)
{
    int minvotes = voter_count;
    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].eliminated == false && candidates[i].votes < minvotes)
        {
            minvotes = candidates[i].votes;
        }
    }
    return minvotes;
}

// Return true if the election is tied between all candidates, false otherwise
bool is_tie(int minvotes)
{
    for (int i = 0; i < candidate_count; i++)
    {
        if (candidates[i].eliminated == false && candidates[i].votes != minvotes)
        {
            return false;
        }
    }
    return true;
}

// Eliminate the candidate (or candidiates) in last place
void eliminate(int minvotes)
{
    for (int i = 0; i < candidate_count; i++)
        if (candidates[i].votes == minvotes)
        {
            candidates[i].eliminated = true;
        }
    return;
}