Union-Find implementation

utilities/python/union_find.py

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+## Union-Find data structure
+## https://en.wikipedia.org/wiki/Disjoint-set_data_structure
+
+parents = [0, 1, 2, 3, 4, 5, 6] # parent[i] is the parent of i
+weights = [1, 1, 1, 1, 1, 1, 1]
+
+def find_root(parents, p):
+    '''Average: O(log n)'''
+    root = p
+    while parents[root] != root:
+        root = parents[root]
+    # Flatten tree
+    while parents[p] != p:
+        parents[p], p = root, parents[p]
+    return root
+
+def union(parents, p, q):
+    '''Average: O(log n)'''
+    p = find_root(parents, p)
+    q = find_root(parents, q)
+    # Link the smaller node to the larger node
+    if weights[p] > weights[q]:
+        parents[q] = p
+        weights[p] += weights[q]
+    else:
+        parents[p] = q
+        weights[q] += weights[p]