排序总结

快速排序：

int partition(int arr[], int left, int right) {
    int i = left, j = right;
    int tmp = arr[left];
    while (i < j) {
        while (i < j && arr[j] > tmp)
            j--;
        if (i < j) {
            arr[i] = arr[j];
            i++;
        }
        while (i < j && arr[i] < tmp)
            i++;
        if (i < j) {
            arr[j] = arr[i];
            j--;
        }
    }
    arr[i] = tmp;
    return i;
}
void quick_sort(int arr[], int left, int right) {
    if(left > right)
        return;
    int j = partition(arr, left, right);
    quick_sort(arr, left, j - 1);
    quick_sort(arr, j + 1, right);
}

---

归并排序：

#include <iostream>
using namespace std;

// 合并数组，排好序，然后在拷贝到原来的数组array
void MergeArray(int array[], int start, int end ,int mid, int temp[]) {
    int i = start;
    int j =  mid + 1;
    int k = 0;
    while (i <= mid && j <= end ) {
        if (array[i] < array[j]) {
            temp[k++] = array[i++];
        }else {
            temp[k++] = array[j++];
        }
    }
    while (i <= mid) {
        temp[k++] = array[i++];
    }
    while (j <= end) {
        temp[k++] = array[j++];
    }
    for (int i = 0; i < k; i ++) {//把temp数组1-k里元素都装到array
        array[start + i] = temp[i];
    }
    
}
// 归并排序，将数组前半部分后半部分分成最小单元，然后在合并
void MergeSort(int array[], int start,  int end, int temp[]) {
    if(start < end) {
        int mid = (start + end)/ 2;
        MergeSort(array, start, mid, temp);
        MergeSort(array, mid + 1, end, temp);
        MergeArray(array, start, end, mid, temp);
    }
    
}
// 在这里创建临时数组，节省内存开销，因为以后的temp都是在递归李使用的。
void MergeSort(int array[], int len) {
    int start = 0;
    int end = len - 1;
    int *temp = new int[len];
    MergeSort(array, start, end, temp);
}

void PrintArray(int array[], int len) {
    for (int i = 0 ; i < len; ++i) {
        cout << array[i] << " " ;
        
    }
    cout << endl;
}

int main(int argc, const char * argv[]) {
    int array[] = {3,5,3,6,7,3,7,8,1};
    
    MergeSort(array, 9);
    PrintArray(array, 9);
    
    
    return 0;
}