Cs50 Tideman Solution May 2026

This is the wall where most students get stuck. The Tideman method requires you to "lock in" the winner of each pair, starting with the strongest victory. Unless... locking that arrow creates a cycle.

A cycle happens if the last arrow points back to a candidate who has already "won" a chain, effectively creating an infinite loop where nobody is the ultimate source.

The Logic: I realized I needed a recursive function. The prompt asks: Does locking this pair create a cycle?

To check this, I wrote a helper function (let's call it creates_cycle).

It looked something like this mentally:

If the cycle is detected, do not lock. If the path ends without hitting the target, lock it in.

We have an election. Voters rank candidates. The Tideman method (a ranked-pair voting system) works like this:

Your job is to write the functions for steps 2, 3, 4, and 5. But step 4—lock_pairs—is where most people get stuck.

To detect a cycle, we use a recursive depth-first search (DFS). The function cycle_check(int start, int end) determines if adding an edge from start to end closes a loop. Cs50 Tideman Solution

We assume pairs is already sorted (by sort_pairs).

void lock_pairs(void)
// Iterate over each pair (strongest to weakest)
    for (int i = 0; i < pair_count; i++)
int winner = pairs[i].winner;
        int loser = pairs[i].loser;
    // If locking this pair does NOT create a cycle
    if (!creates_cycle(winner, loser))
locked[winner][loser] = true;
// Else: skip locking this pair

That’s it. The recursion in creates_cycle handles all chain connections. This is the wall where most students get stuck

The distribution code provides a skeleton with these functions:

The main challenge is lock_pairs. Many students implement everything else correctly but fail cycle detection.

After locking: