【发布时间】：2020-01-07 14:30:25
【问题描述】：
我的代码工作正常，但在创建循环时跳过对的 check50 测试失败。我用来检查周期的逻辑是，在创建从赢家到输家的边缘之前，我从赢家返回边缘并检查它是否曾经到达失败者。如果是这样，则意味着它将创建一个循环，因此跳过边缘但它不起作用。我的逻辑也可能是错误的，如果是这样，请告诉我。这是我的代码-
#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 check_cycle(int n, int m);
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; i++)
{
for (int j = 1; j < candidate_count - i; 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; i++)
{
for (int j = 0; j < candidate_count; 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)
{
// TODO
pair k;
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])
{
//memcpy
k = pairs[i];
pairs[i] = pairs[j];
pairs[j] = k;
}
}
}
return;
}
// Lock pairs into the candidate graph in order, without creating cycles
void lock_pairs(void)
{
// TODO
for (int i = 0; i < pair_count; i++)
{
if (!check_cycle(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)
{
// TODO
for (int i = 0; i < candidate_count; i++)
{
bool source = true;
for (int j = 0; j < candidate_count; j++)
{
if (locked[j][i] == true)
{
source = false;
break;
}
}
if (source == true)
{
printf("%s\n", candidates[i]);
}
}
return;
}
//checking for cycle
bool check_cycle(int n, int m)
{
if (locked[m][n] == true)
{
return true;
}
for (int i = 0; i < candidate_count; i++)
{
if (locked[i][n] == true)
{
check_cycle(i, m);
}
}
return false;
}
【问题讨论】：
-
我不相信问题中有足够的信息。它当然不是 MCVE (Minimal, Complete, Verifiable Example)（或 MRE 或 SO 现在使用的任何名称）或 SSCCE (Short, Self-Contained, Correct Example)。我想也许你的循环检查只寻找长度为 2 的循环（那里和后面），而不是涉及多个步骤的循环。因此，如果您有节点 A->B->C 和 A->D 并添加 C->D，则它可能无法正确检测到（我不确定该示例）。我可能找错树了。