疯子的算法总结(六) 复杂排序算法 ① 归并排序 merge_sort()

#include <bits/stdc++.h>
using namespace std;
void merge(int a[],int n,int left ,int mid,int right);
void merge_sort(int a[],int n,int left,int right);
const int Maxn=5e5;
const int Sentinel=0x3f3f3f3f;
int L[Maxn/2],R[Maxn/2];
int cnt;
int main()
{
    int n;
    int a[1000];
    cin>>n;
    for(int i=0;i<n;i++) cin>>a[i];
    merge_sort(a,n,0,n);
    for(int i=0;i<n;i++) cout<<a[i]<<' ';
}
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]=R[n2]=Sentinel;
    int i=0,j=0;
    for(int k=left;k<right;k++)
    {
        cnt++;
        if(L[i]<R[j]){
            a[k]=L[i++];
        }
        else{
            a[k]=R[j++];
        }
    }
}
void merge_sort(int a[],int n,int left,int right)
{
    if(left<right)
    {
        int mid=(left+right)>>1;
        merge_sort(a,n,left,mid);
        merge_sort(a,n,mid+1,right);
        merge(a,n,left,mid,right);
    }
}

#include <bits/stdc++.h>
using namespace std;
void merge_sort(int a[],int n,int left,int right);
const int Maxn=5e5;
int main()
{
    int n;
    int a[Maxn];
    cin>>n;
    for(int i=0;i<n;i++) cin>>a[i];
    merge_sort(a,n,0,n);
    for(int i=0;i<n;i++) cout<<a[i]<<' ';
}
void merge_sort(int a[],int n,int left,int right)
{
    if(left<right)
    {
        int mid=(left+right)>>1;
        merge_sort(a,n,left,mid);
        merge_sort(a,n,mid+1,right);
        merge(a+left,a+mid+1,a+mid+1,a+right,a+left);
    }
}