Introduction: The Gauntlet of CS50 If you are taking Harvard’s CS50 course, you have likely encountered a common truth: Week 3’s Tideman problem is the first real filter. Many students breeze through plurality, but Tideman—also known as the "ranked pairs" voting method—stops them in their tracks. It is notorious for its complexity, particularly the recursive function required to detect cycles in a graph.
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
If you are stuck, step away, draw graphs, and remember: Master that, and you master Tideman. Introduction: The Gauntlet of CS50 If you are
// Returns true if there is a path from start to end in the locked graph bool is_path(int start, int end) { if (start == end) return true; for (int i = 0; i < candidate_count; i++) { if (locked[start][i] && is_path(i, end)) return true; } return false; } void add_pairs(void) { pair_count = 0; for (int
: If the candidate name is found, set ranks[rank] = candidate_index and return true . Else false .
bool is_path(int start, int end) { if (start == end) return true; for (int i = 0; i < candidate_count; i++) if (locked[start][i] && is_path(i, end)) return true; return false; }