归并排序--迭代&递归写法
作者:
zqw
,
2022-07-29 16:59:50
,
所有人可见
,
阅读 184
#include <iostream>
using namespace std;
const int N = 1e5 + 10;
int n;
int q[N], temp[N];
//合并两个有序子数组
void merge(int l, int mid, int r)
{
int i = l, j = mid + 1;
int k = 0;
while (i <= mid && j <= r)
if (q[i] <= q[j]) temp[k ++ ] = q[i ++ ];
else temp[k ++ ] = q[j ++ ];
while (i <= mid) temp[k ++ ] = q[i ++ ];
while (j <= r) temp[k ++ ] = q[j ++ ];
for (int i = l, j = 0; i <= r; i ++ , j ++ ) q[i] = temp[j];
}
//递归版本
void merge_sort1(int q[], int l, int r)
{
if (l >= r) return;
int mid = l + r >> 1;
merge_sort1(q, l, mid), merge_sort1(q, mid + 1, r);
merge(l, mid, r);
}
//迭代版本
void merge_sort2(int q[])
{
//step表示步长,倍进枚举step
for (int step = 1; step <= n; step *= 2)
{
//offset表示需要合并的区间长度是 step的两倍
int offset = step + step;
//index表示下标。每次合并一个区间长度是offset的子区间,一个offset里有两个step
for (int index = 0; index < n; index += offset) //起点从0开始
{
//在子区间中
int l = index; //左端点
int mid = min(index + step - 1, n - 1); //中点
int r = min(index + offset - 1, n - 1); //右端点
merge(l, mid, r);
}
}
}
int main()
{
cin >> n;
for (int i = 0; i < n; i ++ ) cin >> q[i];
//merge_sort1(q, 0, n - 1);
merge_sort2(q);
for (int i = 0; i < n; i ++ ) cout << q[i] << ' ';
cout << endl;
return 0;
}