static void FindKMostFrequentWords(int k)
{
Node[] nodes = new Node[k];
Node cur = head.next;
//Get 1st K Nodes from linked list: O(k)
int i;
for (i = 0; i < k && cur != null; i++)
{
nodes[i] = cur;
cur = cur.next;
}
//O(n), building a heap
heapify(nodes, i); //place 1st k nodes in min heap, either i is k or i is the total number of words which is < k
while (cur != null)
{
if (cur.count > nodes[0].count)
{
nodes[0] = cur; //O(log n)
heapify(nodes, nodes.Length);
}
cur = cur.next;
}
Console.WriteLine("K most frequently occurring words, where k = {0} are,", k);
foreach (Node n in nodes)
{
Console.WriteLine("{0} : [count = {1}]", n.word, n.count);
}
}
static void AddWord(string s)
{
if (dict.ContainsKey(s))
{
dict[s].count++;
}
else
{
Node n = new Node(s);
dict.Add(s, n);
n.next = head.next;
head.next = n;
}
}
static void siftDown(Node[] nodes, int start, int end)
{
int root = start;
while ((2 * root + 1) <= end)
{
int swap = root;
int child = (2 * root + 1); //get child of the current root node
if (nodes[swap].count > nodes[child].count)
swap = child;
if ((child + 1 <= end) && (nodes[swap].count > nodes[child + 1].count))
swap = child + 1;
if (swap != root)
{
Node temp = nodes[swap];
nodes[swap] = nodes[root];
nodes[root] = temp;
root = swap;
}
else
return;
}
}
public Node(string word, int count, Node next)
{
this.word = word;
this.count = count;
this.next = next;
}
static void heapify(Node[] nodes, int count)
{
int end = count - 1; //count is total number of nodes in the array, which is k.
int start = (end - 1) / 2; //get parent of last but one child, that is the last parent in the array
while (start >= 0)
{
siftDown(nodes, start, end); //end is the index of last node in the array
start--;
}
}