快速排序（殷人昆版）

快速排序的基本思想：任取待排序元素序列中的某个元素（例如取第一个元素）作为基准，按照该元素的排序码大小，将整个元素序列划分为左右两个子序列；左侧子序列中元素的排序码都小于基准元素的排序码，右侧子序列中的元素的排序码都大于基准元素的排序码。然后在左右序列中重复这种操作。

void Swap(int& a, int& b){int tmp = a;a = b;b = tmp;}int Partition(int V[], int low, int high){int privotpos = low;int privot = V[low];for(int i = low+1; i < high+1; ++i){if(V[i] < privot){privotpos++;if(privotpos != i){Swap(V[privotpos],V[i]);}}}V[low] = V[privotpos];V[privotpos] = privot;return privotpos;}void QuickSort(int V[], const int left, const int right){if(left < right){int privotpos = Partition(V, left, right);QuickSort(V,left, privotpos-1);QuickSort(V,privotpos+1, right);}}

快速排序的改进算法：当序列长度M取值为5~25时，采用直接插入排序比全部使用快速排序快10%

#define M 5

void QuickSort_insertSort(int V[], const int left, const int right){if(right-left <= M){InsertSort(V, left, right);}if(left < right){int privotpos = Partition(V, left, right);QuickSort(V,left, privotpos-1);QuickSort(V,privotpos+1, right);}}

void QuickSort(int V[], const int left, const int right){if(left < right){int privotpos = Partition(V, left, right);QuickSort(V,left, privotpos-1);QuickSort(V,privotpos+1, right);}}

void InsertSort(int V[], const int left, const int right){int i, j;for(i = left+1; i < right+1; ++i){if(V[i] < V[i-1]){int tmp = V[i];j = i-1;do{V[j+1] = V[j];j--;}while(j >= left && tmp < V[j]);//向后移位V[j+1] = tmp;}}}

快速—直接插入混合排序算法

void NewQuickSort(int V[], const int left, const int right){if(right-left <= M){return;}if(left < right){int privotpos = Partition(V, left, right);NewQuickSort(V,left, privotpos-1);NewQuickSort(V,privotpos+1, right);}}void HybirdSort(int V[], const int left, const int right){NewQuickSort(V, left, right);InsertSort(V, left, right);}

三者中取中算法来实现快速排序基准位

int median3(int V[], int left, int right){int mid = (left+right)/2;int k = left;if(V[mid] < V[k]){k = mid;}if(V[right] < V[k]){k = right;//k指向三者中最小值}if(k != left){Swap(V[k], V[left]);}if(mid != right && V[mid] < V[right]){Swap(V[mid], V[right]);}return V[right];}//一趟划分算法的实现int Partition_3(int V[], int left, int right){int i = left, j = right-1;if(left < right){int privot = median3(V, left, right);while(1){while(i<j && V[i] < privot)//正向，小于privot的留在左侧，一旦大于等于privot停步{i++;}while(i<j && privot < V[j])//反向，大于privot的留在右侧，一旦小于等于privot停步{j--;}if(i < j)//比privot小的交换到左侧，比privot大的交换到右侧{Swap(V[i], V[j]);i++;j--;}else//i=j表明一趟检测完成，终止循环{break;}}if(V[i] > privot)//privot移到它排序后应该在的位置{V[right] = V[i];V[i] = privot;}}return i;}void NewQuickSort_3(int V[], const int left, const int right)//三者中取中值放在最右端{if(right-left <= M){return;}if(left < right){int privotpos = Partition_3(V, left, right);QuickSort(V,left, privotpos-1);QuickSort(V,privotpos+1, right);}}void HybirdSort_3(int V[], const int left, const int right){NewQuickSort(V, left, right);InsertSort(V, left, right);}

三路划分的快速排序算法

void QuickSortNew(int V[], int left, int right){int i, j, k, p, q;int privot = V[right];if(right <= left){return;}i = left-1;j = right;p = left-1;q = right;while(1){while(V[++i] < privot){if(i == j){break;}}while(privot < V[--j]){if(j == i){break;}}if(i >= j){break;}Swap(V[i], V[j]);if(V[i] == privot){p++;Swap(V[p], V[i]);}if(privot == V[j]){q--;Swap(V[q], V[j]);}}if(V[i] > V[right]){Swap(V[i], V[right]);k = right-1;}else{k = right;}j--;i++;while(k >= q){Swap(V[k], V[i]);k--;i++;}for(k = left; k < p+1; k++, j--){Swap(V[k], V[j]);}QuickSortNew(V, left, j);QuickSortNew(V, i, right);}