Friend Groups - Amazon Top Interview Questions
Problem Statement :
You are given an undirected graph friends as an adjacency list, where friends[i] is a list of people i is friends with. Friendships are two-way. Two people are in a friend group as long as there is some path of mutual friends connecting them.
Return the total number of friend groups.
Constraints
n ≤ 250 where n is the length of friends
Example 1
Input
friends = [
[1],
[0, 2],
[1],
[4],
[3],
[]
]
Output
3
Explanation
The three friend groups are
[0, 1, 2]
[3, 4]
[5]
Solution :
Solution in C++ :
int find(int x, vector<int>& parent) {
if (parent[x] == -1) return x;
return find(parent[x], parent);
}
void unionn(int x, int y, vector<int>& parent) {
int a = find(x, parent);
// cout<<a<<" ";
int b = find(y, parent);
// cout<<b<<endl;
if (a == b) return;
parent[b] = a;
}
int solve(vector<vector<int>>& f) {
if (f.empty()) return 0;
int maxx = INT_MIN;
for (int i = 0; i < f.size(); i++) {
for (int j = 0; j < f[i].size(); j++) {
maxx = max(f[i][j], maxx);
}
}
vector<int> p(maxx + 1, -1);
vector<int> v;
for (int i = 0; i < f.size(); i++) {
if (f[i].size() == 0 || f.size() == 1) continue;
for (int j = 1; j < f[i].size(); j++) {
// cout<<f[i][0]<<" "<<f[i][j]<<endl;
unionn(f[i][0], f[i][j], p);
}
}
int count = 0;
for (int i = 0; i < p.size(); i++) {
if (p[i] == -1) count++;
// cout<<p[i]<<" ";
}
return count;
}
Solution in Python :
class DSU:
def __init__(self, n):
self.parent = [i for i in range(n)]
self.rank = [0 for i in range(n)]
def find(self, x):
if self.parent[x] == x:
return self.parent[x]
self.parent[x] = self.find(self.parent[x])
return self.parent[x]
def union(self, u, v):
pu = self.find(u)
pv = self.find(v)
if self.rank[pu] < self.rank[v]:
pu, pv = pv, pu
self.parent[pv] = pu
self.rank[pu] += self.rank[pv]
def count(self):
par_set = set()
for parent in self.parent:
par_set.add(self.find(parent))
return len(par_set)
class Solution:
def solve(self, A):
n = len(A)
dsu = DSU(n)
for user, friends in enumerate(A):
for friend in friends:
dsu.union(user, friend)
return dsu.count()
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