if (locked[from][i] && can_reach(i, target)) return true;
The Tideman problem is challenging precisely because it requires understanding graph theory concepts and recursive algorithms. However, by breaking down the problem into these six functions and understanding what each one accomplishes, you can build a complete solution that correctly implements the ranked pairs voting method.
This article is not just about providing code to copy-paste. It is about understanding why the Tideman solution works, how to avoid the common pitfalls, and how to implement the lock_pairs function and cycle detection correctly.
void record_preferences(int ranks[])
: Validates a voter's choice by checking if the name exists in the candidates array and updates the ranks array.
// Get the names of the candidates Candidate candidates[num_candidates]; for (int i = 0; i < num_candidates; i++) printf("Enter candidate %d: ", i+1); scanf("%s", candidates[i].name); candidates[i].votes = 0;
This function fills the pairs array with matchups where one candidate beats another. Compare preferences[i][j] with preferences[j][i] . Cs50 Tideman Solution
The Tideman method (also known as ranked pairs) is a preferential voting system. Unlike simply counting who got the most first-place votes, Tideman ensures that the winner is the candidate who beats everyone else in head-to-head matchups, even if they aren't the top choice of the majority. The algorithm works in three main steps:
Basic cycle detection that only looks one step ahead fails to catch longer cycles. For example, A→B, B→C, then checking A→C: you need to see that C→A through A→B→C is a cycle.
After identifying all winner-loser pairs, you store them in a pairs array. Each pair struct contains a winner index and a loser index. CS50 Tideman - Dev Genius It is about understanding why the Tideman solution
// Function to recount votes void recount_votes(voter_t *voters_prefs, int voters, candidate_t *candidates_list, int candidates) // Recount votes for (int i = 0; i < voters; i++) for (int j = 0; j < candidates; j++) if (candidates_list[voters_prefs[i].preferences[j] - 1].votes == 0) // Move to next preference voters_prefs[i].preferences[j] = -1; else break;
To detect a cycle, use a recursive function (often called has_cycle). This function should: Take a starting candidate and a target candidate. Check if the target is already locked to the starter.
: Updates a 2D array, preferences[i][j] , which tracks how many voters prefer candidate i over candidate j . 2. Identifying Winners ( add_pairs ) Compare preferences[i][j] with preferences[j][i]
is_source = false; break;