Various sort notes---based on the Compare sort section

1. Merge sort

Merge sort is based on a strategy called "divide and conquer".

Sort List

Sort a linked list in O(n log n) time using constant space Complexity.

Method 1:merge sort, in the way of divide and conquer, first divides the list into the left and right parts, and then sorts the merged

sort list (divide and Conquer)

2. Quick Sort

Pseudo Code:

function quicksort (q)     var list less, pivotlist, greater     if length (q) ≤1 {         return q     } Else {         Select a Pivot value pivot from Q for each         x in Q except the pivot element             if x < pivot then add X to less             if X≥pi Vot then add x to greater         add pivot to pivotlist         return concatenate (quicksort (less), pivotlist, quicksort (greater ))     }

LinkedList Quick Sort

 public classSolution { publicListNode sortlist (listnode head) {if(head = =NULL|| Head.next = =NULL) {            returnhead; } ListNode Mid= Findmedian (head);//O (n)//new three Dummmy node with a tail point to itListNode Leftdummy =NewListNode (0), Lefttail =leftdummy; ListNode Rightdummy=NewListNode (0), Righttail =rightdummy; ListNode Middledummy=NewListNode (0), Middletail =middledummy; //Sprate to three part         while(head! =NULL) {            if(head.val <Mid.val) {lefttail.next=head; Lefttail=head; } Else if(head.val >Mid.val) {righttail.next=head; Righttail=head; } Else{middletail.next=head; Middletail=head; } head=head.next; }                //Make the tail to nullLefttail.next =NULL; Middletail.next=NULL; Righttail.next=NULL; //recurisive do the sortListNode left =sortlist (leftdummy.next); ListNode right=sortlist (rightdummy.next); //connect the three parts together        returnconcat (left, middledummy.next, right); }    Private Staticlistnode Findmedian (listnode head) {listnode Fast=head.next; ListNode Slow=head;  while(fast! =NULL&& fast.next! =NULL) {slow=slow.next; Fast=fast.next.next; }        returnslow; }    Private Staticlistnode concat (listnode left, listnode mid, listnode right) {listnode dummy=NewListNode (0), Dummytail =dummy; Dummytail=Connect (dummytail, left); Dummytail=Connect (dummytail, mid); Dummytail=Connect (dummytail, right); returndummy.next; }    Private StaticListNode Connect (listnode dummytail, listnode Current) { while(current! =NULL) {dummytail.next=current ; Dummytail=dummytail.next; current=current.next; }         returndummytail; }}

sortlist

Various sort notes---based on the Compare sort section