归并排序 ALDS1_5_B:Merge Sort

Merge Sort

Write a program of a Merge Sort algorithm implemented by the following pseudocode. You should also report the number of comparisons in the Merge function.

Merge(A, left, mid, right)
  n1 = mid - left;
  n2 = right - mid;
  create array L[0...n1], R[0...n2]
  for i = 0 to n1-1
    do L[i] = A[left + i]
  for i = 0 to n2-1
    do R[i] = A[mid + i]
  L[n1] = SENTINEL
  R[n2] = SENTINEL
  i = 0;
  j = 0;
  for k = left to right-1
    if L[i] <= R[j]
      then A[k] = L[i]
           i = i + 1
      else A[k] = R[j]
           j = j + 1

Merge-Sort(A, left, right){
  if left+1 < right
    then mid = (left + right)/2;
         call Merge-Sort(A, left, mid)
         call Merge-Sort(A, mid, right)
         call Merge(A, left, mid, right)

Input

In the first line n is given. In the second line, n integers are given.

Output

In the first line, print the sequence S. Two consequtive elements should be separated by a space character.

In the second line, print the number of comparisons.

Constraints

• n ≤ 500000
• 0 ≤ an element in S ≤ 109

Sample Input 1

10
8 5 9 2 6 3 7 1 10 4

Sample Output 1

1 2 3 4 5 6 7 8 9 10
34
又抄了一份题解（那个34是归并排序比较的次数）代码如下

#include<iostream>
#include<cstring>
#include<stack>
#include<cstdio>
#include<cmath>
using namespace std;
#define MAX 500000
#define INF 2e9
int L[MAX/2+2],R[MAX/2+2];
int cnt;
void merge(int A[],int n,int left,int mid,int right)
{
    int n1=mid-left;
    int n2=right-mid;
    for(int i=0;i<n1;i++)
    {
        L[i]=A[left+i];
    }
    for(int i=0;i<n2;i++)
    {
        R[i]=A[mid+i];
    }
    L[n1]=INF;
    R[n2]=INF;
    int i=0,j=0;
    for(int k=left;k<right;k++)//合并
    {
     cnt++;
     if(L[i]<=R[j])
     A[k]=L[i++];
     else
     A[k]=R[j++];
}
}
void mergeSort(int A[],int n,int left,int right)
{
    if(left+1<right)
    {
        int mid=(left+right)/2;
        mergeSort(A,n,left,mid);
        mergeSort(A,n,mid,right);
        merge(A,n,left,mid,right); 
    }
}
int main()
{
int A[MAX],n;
cnt=0;
cin>>n;
for(int i=0;i<n;i++)
cin>>A[i];
mergeSort(A,n,0,n);
for(int i=0;i<n;i++)
{
    if(i)
    cout<<" ";
    cout<<A[i];
}
cout<<endl;
cout<<cnt<<endl;
return 0;
 }