Merge sort for reverse order

We know that the most typical method for reverse order is the tree array, but there is another way to do this is Merge_sort (), which is the merge sort.

In fact, the number of exchanges in the merge sort is the inverse of the array, for what?

We can consider this:

The merge sort is to divide the series A[l,h] into two halves a[l,mid] and a[mid+1,h], respectively, and then combine the two halves together.

In the process of merging (set L<=i<=mid,mid+1<=j<=h), when A[i]<=a[j], no reverse order is generated; when A[i]>a[j], the

The first half of the number is larger than a[i] larger than a[j], will a[j] in front of a[i], reverse order number to add mid+1-i. As a result, you can merge

Calculates the number of reverse orders in the merge process in the sort.

Title: http://poj.org/problem?id=1804

Test Instructions: given a sequence of a[], it is allowed to exchange only two adjacent digits at a time, at least how many times it is exchanged to turn it into a non-degradation sequence.

1#include <iostream>2#include <string.h>3#include <stdio.h>4 5 using namespacestd;6 Const intN =1005;7 8 intA[n],tmp[n];9 intans;Ten  One voidMerge (intLintMintR) A { -     inti =l; -     intj = m +1; the     intK =l; In particular, K is started from L (letter) and not 0; -      while(I <= m && J <=R) -     { -         if(A[i] >A[j]) +         { -tmp[k++] = a[j++]; +Ans + = m-i +1; A         } at         Else -         { -tmp[k++] = a[i++]; -         } -     } -      while(i <= m) tmp[k++] = a[i++]; in      while(J <= r) tmp[k++] = a[j++]; -      for(inti=l;i<=r;i++)//must remember to copy the TMP element to a when the merge is complete toA[i] =Tmp[i]; + } -  the voidMerge_sort (intLintR) * { $     if(L <R)Panax Notoginseng     { -         intm = (L + r) >>1; the Merge_sort (l,m); +Merge_sort (m+1, R); A Merge (l,m,r); the     } + } -  $ intMain () $ { -     intn,t,tt=1; -scanf"%d",&T); the      while(t--) -     {Wuyiscanf"%d",&n); the          for(intI=0; i<n;i++) -scanf"%d",&a[i]); WuAns =0; -Merge_sort (0, N-1); Aboutprintf"Scenario #%d:\n%d\n\n", tt++, ans); $     } -     return 0; -}

Transferred from: http://blog.csdn.net/acdreamers/article/details/16849761

Merge sort for reverse order