【哈佛cs50 2022】lab3 & problemSet3【ing】

（1）lab3

如何测试每个代码运行所需要的时间？time ./sort1 sorted5000.txt

（2）problem set3 - plurality

#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)
{
    // TODO
    int compare = 0;
    for(int i=0;i<candidate_count;++i){
        compare = strcmp(candidates[i].name,name);
        if(!compare){
            candidates[i].votes+=1;
            //printf("compare result-%i,votes-%i\n",strcmp(candidates[i].name,name),candidates[i].votes);
            return true;
        }
    }
    return false;
}

// Print the winner (or winners) of the election
void print_winner(void)
{
    // TODO
    int sort_max = 0;
    if(candidate_count == 1){
        printf("%s\n",candidates[candidate_count-1].name);
    }
    else{
        sort_max = candidates[0].votes;
        for(int i=0;i<candidate_count-1;++i){
            if(candidates[i+1].votes > candidates[i].votes){
                sort_max = candidates[i+1].votes;
            }
        }
        //printf("%i\n",sort_max);
        for(int j=0;j<candidate_count;++j){
            if(candidates[j].votes == sort_max){
                printf("%s\n",candidates[j].name);
            }
        }
    }
    return;
}

（3）runoff

#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)
    {
        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
//voter:voter_count-ing
//rank:candidate_count-ing
bool vote(int voter, int rank, string name)
{
    // TODO
    for(int i=0;i<candidate_count;i++){
        if(!strcmp(name,candidates[i].name)){
            preferences[voter][rank] = i;
            return true;
        }
    }

    return false;
}

// Tabulate votes for non-eliminated candidates
void tabulate(void)
{
    // TODO
    int rank = 0;
    int number = 0;
    int count = 0;
    int mid = 0;
    while(count<voter_count){

        for(int j=0;j<voter_count;j++){
            rank = 0;
            for(int i=0;i<candidate_count;i++){
                mid = preferences[j][i];
                if(!candidates[mid].eliminated){
                    break;
                }
                rank ++;
            }
            number = preferences[j][rank];
            candidates[number].votes ++;
            count++;
        }
    }
    return;
}

// Print the winner of the election, if there is one
bool print_winner(void)
{
    // TODO
    int win_number = 0.5 * voter_count;
    int max = candidates[0].votes;
    int index = 0;
    for(int i=1;i<candidate_count;i++){
        if(candidates[i].votes > max){
            max = candidates[i].votes;
            index = i;
        }
        else if(candidates[i].votes == max){
            return false;
        }
        else{
            continue;
        }
    }
    int leader = candidates[index].votes;
    printf("leader-%i-%s\n",index,candidates[index].name);
    for(int i=0;i<candidate_count;i++){
        if(i==index){
            continue;
        }
        if(max==candidates[i].votes){
            return false;
        }
    }
    if(leader>win_number){
        printf("%s\n",candidates[index].name);
        return true;
    }
    else{
        return false;
    }
    return false;
}

// Return the minimum number of votes any remaining candidate has
int find_min(void)
{
    // TODO
    int min = candidates[0].votes;

    for(int j=1;j<candidate_count;j++){
        if(!candidates[j].eliminated){
            if(candidates[j].votes<min){
                min = candidates[j].votes;
            }
        }
    }
    return min;
}

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

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

    return;
}

（4）Tideman-ing