1、算法思路(分治策略)
(1)劃分:將待排序序列r1, r2, …, rn劃分爲兩個長度相等的子序列r1, …, rn/2和rn/2+1, …, rn;
(2)求解子問題:分別對這兩個子序列進行排序,得到兩個有序子序列;
(3)合併:將這兩個有序子序列合併成一個有序序列。
2、代碼實現
void mergeArray(int data[], int first, int mid, int last, int temp[])//一趟合併兩個子序列
{
int i = first, j = mid + 1, k = 1;
while (i <= mid && j <= last)
{
if (data[i] <= data[j])
temp[k++] = data[i++];
else
temp[k++] = data[j++];
}
while (i <= mid) temp[k++] = data[i++];
while (j <= last) temp[k++] = data[j++];
for (i = 0; i < k - 1; ++i) //將排好的數據拷貝回去
data[first + i] = temp[i + 1]; //temp下標從1開始
}
void mergeSort(int data[], int first, int last, int temp[])
{
if (last > first)
{
int mid = (last + first) / 2;
mergeSort(data, first, mid, temp);
mergeSort(data, mid + 1, last, temp);
mergeArray(data, first, mid, last, temp);
}
}
int main(int argc, char *argv[])
{
int data[20] = { 0, 1, 7, 3, 50, 43, 34, 78, 23, 67, 90 }; //第0個位置不用
int temp[20]; //第0個位置不用
mergeSort(data, 1, 10, temp);
int i = 1;
while (i <= 10) //輸出
{
cout << data[i] << ' ';
++i;
}
system("pause");
return 0;
}