// ... (implement all functions as described above) ...
void lock_pairs(void) { for (int i = 0; i < pair_count; i++) { int w = pairs[i].winner; int l = pairs[i].loser;
void add_pairs(void) { pair_count = 0; for (int i = 0; i < candidate_count; i++) { for (int j = i + 1; j < candidate_count; j++) { if (preferences[i][j] > preferences[j][i]) { pairs[pair_count].winner = i; pairs[pair_count].loser = j; pair_count++; } else if (preferences[j][i] > preferences[i][j]) { pairs[pair_count].winner = j; pairs[pair_count].loser = i; pair_count++; } // ties are ignored } } return; } Sort pairs in descending order of victory margin: margin = preferences[winner][loser] - preferences[loser][winner] . Cs50 Tideman Solution
: The problem requires that each pair appears only once, with the winner first.
int voter_count = get_int("Number of voters: "); for (int i = 0; i < voter_count; i++) { int ranks[candidate_count]; 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; } Mistake 1: Incorrect Cycle Detection Logic Many students try to detect cycles by checking if locked[loser][winner] already exists. That is wrong. A cycle can be longer than two edges (A→B→C→A). Always use DFS. Mistake 2: Modifying the pairs array in sort_pairs Ensure you sort descending . Reversing the comparison sign is a common typo. Mistake 3: Forgetting to reset pair_count In add_pairs , reset pair_count = 0 before adding new pairs. Mistake 4: Stack overflow in recursion The recursive is_path function is safe for up to 9 candidates. For larger sets, use an iterative DFS, but CS50’s MAX is 9. Mistake 5: Off-by-one in record_preferences Ensure inner loop starts at j = i + 1 , not j = 0 . 6. Testing Your Solution Run the provided tideman tests from CS50’s check50: : The problem requires that each pair appears
#include <cs50.h> #include <stdio.h> #include <string.h> #define MAX 9
void record_preferences(int ranks[]) { for (int i = 0; i < candidate_count; i++) { for (int j = i + 1; j < candidate_count; j++) { int winner = ranks[i]; int loser = ranks[j]; preferences[winner][loser]++; } } return; } We need to populate the global pairs array. A pair exists if preferences[i][j] > preferences[j][i] . If equal (tie), skip. A cycle can be longer than two edges (A→B→C→A)
: Loop through all pairs of candidates in the ranking. If i is before j in ranks , then preferences[ranks[i]][ranks[j]]++ .