[hackerrank] merging_communities

jlas · jlas · commit d7ab9fbf55a8 · 2016-10-11T23:55:09.000-04:00
diff --git a/hackerrank/merging_communities/README.md b/hackerrank/merging_communities/README.md
@@ -0,0 +1,43 @@
+# Merging Communities
+
+People connect with each other in a social network. A connection between
+Person I and Person J is represented as M I J. When two persons belonging to
+different communities connect, the net effect is the merger of both
+communities which I and J belongs to.
+
+At the beginning, there are N people representing N communities. Suppose
+person 1 and 2 connected and later 2 and 3 connected, then 1, 2, and 3 will
+belong to the same community.
+
+There are two type of queries:
+
+1. M I J => communities containing person I and J merged (if they belong to
+different communities).
+
+2. Q I => print the size of the community to which person I belongs.
+
+## Input format
+
+The first line of input will contain integers N and Q, i.e. the number of
+people and the number of queries. The next Q lines will contain the queries.
+
+## Output format
+
+The output of the queries.
+
+## Sample input
+
+    3 6
+    Q 1
+    M 1 2
+    Q 2
+    M 2 3
+    Q 3
+    Q 2
+
+## Sample output
+
+    1
+    2
+    3
+    3
diff --git a/hackerrank/merging_communities/merging_communities.py b/hackerrank/merging_communities/merging_communities.py
@@ -0,0 +1,49 @@
+#!/bin/python
+
+# Use quick-union approach described here:
+#   https://www.cs.princeton.edu/~rs/AlgsDS07/01UnionFind.pdf
+
+from collections import deque
+
+N, Q = map(int,input().strip().split(' '))
+
+# 1st index is dummy placeholder since input is 1-indexed
+s = [i for i in range(N+1)]
+cnt = [0]+[1 for i in range(N)]
+
+# follow parent indices to root, store intermediates in list
+def findparent(c, d):
+    while c != s[c]:
+        d.append(c)
+        c = s[c]
+    return c
+
+# set all intermediate indices to parent
+def percolate(p, d):
+    for i in d:
+        s[i] = p
+
+for i in range(Q):
+    inpt = input().strip().split(' ')
+    qry = inpt[0]
+    a = sorted(map(lambda x: int(x),inpt[1:]))
+    i0 = a[0]
+
+    if qry == 'Q':
+        if i0 != s[i0]:
+            d = deque()
+            i0 = findparent(i0, d)
+            percolate(i0, d)
+        print(cnt[i0])
+        continue
+
+    # qry == 'M'
+    i1 = a[1]
+    if s[i0] != s[i1]:
+        d = deque()
+        i0 = findparent(i0, d)
+        i1 = findparent(i1, d)
+        if s[i0] != s[i1]:
+            cnt[i0] += cnt[i1]
+            d.append(i1)
+            percolate(i0, d)
