重温归并排序

分成小块，回溯时合并

#include <bits/stdc++.h>
#define dbug(x) cout << #x << "=" << x << endl
#define eps 1e-8
#define pi acos(-1.0)
 
using namespace std;
typedef long long LL;
 
const int inf = 0x3f3f3f3f;
 
template<class T>inline void read(T &res)
{
   char c;T flag=1;
   while((c=getchar())<'0'||c>'9')if(c=='-')flag=-1;res=c-'0';
   while((c=getchar())>='0'&&c<='9')res=res*10+c-'0';res*=flag;
}

const int maxn = 2e5 + 7;

int a[10];

void Sort(int, int);

void merge(int l, int r) {
    if(l >= r) return;
    int mid = (l + r) >> 1;
    merge(l, mid);
    merge(mid + 1, r);
    Sort(l, r);
}

void Sort(int l, int r) {
    vector<int> temp;
    int mid = (l + r) >> 1;
    int i = l, j = mid + 1;
    while(i <= mid && j <= r) {
        if(a[i] < a[j]) {
            temp.push_back(a[i]);
            ++i;
        }
        else {
            temp.push_back(a[j]);
            ++j;
        }
    }
    while(i > mid && j <= r) {
        temp.push_back(a[j++]);
    }
    while(i <= mid && j > r) {
        temp.push_back(a[i++]);
    }
    for (int i = 0; i < r - l + 1; ++i) {
        a[i + l] = temp[i];
    }
}

int main()
{
    for (int i = 0; i < 10; ++i) {
        a[i] = 9 - i;
    }
    cout << "The initial array: ";
    for ( int i = 0; i <= 9; ++i ) {
        cout << a[i] << ' ';
    }
    cout << endl;
    merge(0, 9);
    cout << "The final array: ";
    for (int i = 0; i <= 9; ++i) {
        cout << a[i] << ' ';
    }
    cout << endl;
    return 0;
}