/// <summary>
/// Leetcode 721
/// https://leetcode.com/problems/accounts-merge/
/// </summary>
/// <param name="accounts"></param>
/// <returns></returns>
public static IList <IList <string> > AccountsMerge(IList <IList <string> > accounts)
{
var emailSet = getAllEmails(accounts);
// https://leetcode.com/problems/accounts-merge/discuss/164699/C-Solution-(Union-Find)-beats-91.49
var emailList = emailSet.ToList();
var ordCmp = StringComparer.Ordinal;
emailList.Sort(ordCmp);
var emailNameMap = getEmailNameMap(accounts);
var emailIdmap = new Dictionary <string, int>();
int index = 0;
var emailLookup = new List <string>();
foreach (var item in emailList)
{
emailIdmap.Add(item, index);
index++;
emailLookup.Add(item);
}
var unionFind = new QuickUnion(emailSet.Count);
unionFind.EmailIdMap = emailIdmap;
foreach (var list in accounts)
{
for (int i = 1; i < list.Count - 1; i++)
{
var email1 = list[i];
var email2 = list[i + 1];
var connected = unionFind.Connected(email1, email2);
if (!connected)
{
unionFind.Union(email1, email2);
}
}
}
// flat the tree
for (int i = 0; i < emailSet.Count; i++)
{
unionFind.QuickFindAndPathCompression(i);
}
var dict = new Dictionary <int, List <string> >();
var parent = unionFind.GetParent();
for (int i = 0; i < parent.Length; i++)
{
var key = parent[i];
if (!dict.ContainsKey(key))
{
dict.Add(key, new List <string>());
}
dict[key].Add(emailLookup[i]);
}
// output a list
var result = new List <IList <string> >();
foreach (var item in dict.Keys)
{
var list = new List <string>();
var email = emailLookup[item];
var name = emailNameMap[email];
list.Add(name);
var values = dict[item];
list.AddRange(values);
result.Add(list);
}
return(result);
}
