From 9b38f4a68773bb08fe923136c9faeade6a9794e9 Mon Sep 17 00:00:00 2001
From: Haidong Ji
Date: Mon, 4 Mar 2019 20:51:19 -0600
Subject: Merging tables done.

Not too bad since I worked it out in Java. A bit surprised that
Python class is used in starter file, but I made it testable
and wrote test cases. All is well.
---
 sources/merging_tables.py | 56 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 sources/merging_tables.py

(limited to 'sources')

diff --git a/sources/merging_tables.py b/sources/merging_tables.py
new file mode 100644
index 0000000..985316e
--- /dev/null
+++ b/sources/merging_tables.py
@@ -0,0 +1,56 @@
+# python3
+
+
+class Database:
+    def __init__(self, row_counts):
+        self.row_counts = row_counts
+        self.max_row_count = max(row_counts)
+        n_tables = len(row_counts)
+        self.ranks = [1] * n_tables
+        self.parents = list(range(n_tables))
+        self.set_id = list(range(n_tables))
+
+    def find(self, i):
+        if i != self.parents[i]:
+            self.parents[i] = self.find(self.parents[i])
+        return self.parents[i]
+
+    def merge(self, src, dst):
+        real_dst = self.find(dst)
+        real_src = self.find(src)
+        if real_dst == real_src:
+            return
+        self.max_row_count = max(self.max_row_count,
+                                 self.row_counts[self.set_id[real_dst]] + self.row_counts[self.set_id[real_src]])
+        self.row_counts[real_dst] = self.row_counts[self.set_id[real_dst]] + self.row_counts[self.set_id[real_src]]
+        self.row_counts[real_src] = 0
+        self.set_id[real_src] = real_dst
+        self.set_id[real_dst] = real_dst
+        self.union(src, dst)
+
+    def union(self, src, dst):
+        destination_id = self.find(dst)
+        source_id = self.find(src)
+        if destination_id == source_id:
+            return
+        if self.ranks[destination_id] > self.ranks[source_id]:
+            self.parents[source_id] = destination_id
+        else:
+            self.parents[destination_id] = source_id
+            if self.ranks[destination_id] == self.ranks[source_id]:
+                self.ranks[source_id] = self.ranks[source_id] + 1
+
+
+def main():
+    n_tables, n_queries = map(int, input().split())
+    counts = list(map(int, input().split()))
+    assert len(counts) == n_tables
+    db = Database(counts)
+    for i in range(n_queries):
+        dst, src = map(int, input().split())
+        db.merge(dst - 1, src - 1)
+        print(db.max_row_count)
+
+
+if __name__ == "__main__":
+    main()
-- 
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