Trace n = 6, edges = [[0,1],[0,2],[3,5],[5,4],[4,3]].
Initially: each node is its own parent.
Union(0,1): parent[1] = 0. Components: {0,1}, {2}, {3}, {4}, {5}.
Union(0,2): parent[2] = 0. Components: {0,1,2}, {3}, {4}, {5}.
Union(3,5): parent[5] = 3. Components: {0,1,2}, {3,5}, {4}.
Union(5,4): find(5)=3, parent[4] = 3. Components: {0,1,2}, {3,4,5}.
Union(4,3): find(4)=3, find(3)=3. Already same. No change.
Check: find(0) = 0, find(5) = 3. Different. Return false.
time where is inverse Ackermann (nearly constant). space.