各种排序算法实现

1. 归并排序算法：

非递归实现：

void mergeSort(vector<int> & nums, vector<int> &tmpNums, int left, int right, int end)//right为右边一段数据的开始，同时也可以用来判断左边一段数据的结束，并且左边的数组长度总是大于或等于右边数组长度{int idx_left=left;int idx_right=right;int idx_total=left;while(idx_left<right && idx_right<=end){if(nums[idx_left]<=nums[idx_right])tmpNums[idx_total++]=nums[idx_left++];elsetmpNums[idx_total++]=nums[idx_right++];}while(idx_left<right)tmpNums[idx_total++]=nums[idx_left++];while(idx_right<=end)tmpNums[idx_total++]=nums[idx_right++];idx_left=left;while(idx_left<=end){nums[idx_left]=tmpNums[idx_left];idx_left++;}}void merge(vector<int> & nums, vector<int> & tmpNums){int step=1;int i;int n=nums.size();while(step<n){for(i=0; i<=n-2*step; i+=2*step)//注意，这里i<=n-2*step是因为要保证最后的一对step数组能够正确排序{mergeSort(nums, tmpNums, i, i+step, i+2*step-1);}if(i<n-step)mergeSort(nums, tmpNums, i, i+step, n-1);//对于最后不能正好是一对step长度的情况，要单独处理，且保证最后一个参数为n-1step*=2;}}

对于上面的函数merge,还可以写成下面的形式

void nMergeSort(vector<int>& nums){vector<int> vec(nums.size());int end=nums.size()-1;for(int s=1; s<nums.size(); s<<=1){for(int i=0; i+s<=end; i+=(2*s)){if(i+2*s-1<=end)merge(nums, vec, i, i+s, i+2*s-1);elsemerge(nums, vec, i, i+s, end);}}}

递归实现方式：

void mergeSort(vector<int> & nums, vector<int> &tmpNums, int left, int right, int end){int idx_left=left;int idx_right=right;int idx_total=left;while(idx_left<right && idx_right<=end){if(nums[idx_left]<=nums[idx_right])tmpNums[idx_total++]=nums[idx_left++];elsetmpNums[idx_total++]=nums[idx_right++];}while(idx_left<right)tmpNums[idx_total++]=nums[idx_left++];while(idx_right<=end)tmpNums[idx_total++]=nums[idx_right++];idx_left=left;while(idx_left<=end){nums[idx_left]=tmpNums[idx_left];idx_left++;}}void merge(vector<int> & nums, vector<int> & tmpNums, int left, int right){if(left<right){int mid=(left+right)/2;merge(nums, tmpNums, left, mid);merge(nums, tmpNums, mid+1, right);//注意mid+1mergeSort(nums, tmpNums, left, mid+1, right);}}

2. 快速排序

void quikSort(vector<int>&nums, int low, int high){if(low>=high)return;int key=nums[low];int start=low, end=high;while(start<end){//这里判断start<end不是<=while(end>start && nums[end]>key)end--;nums[start]=nums[end];//赋值的操作方法while(start<end && nums[start]<=key)start++;nums[end]=nums[start];//赋值的操作方法}nums[start]=key;//最后记得修改start下标对应的值quikSort(nums, low, start-1);quikSort(nums, start+1, high);}

更高效的快排算法：

void mSwap(int & a, int & b){        int tmp=a;        a=b;        b=tmp;    }        void myQsort(vector<int> &nums, int low, int high){        if(low>=high)            return ;        int left=low, right=high;        int mid=(low+high)>>1;                int key=max(nums[low], nums[mid]);//增加计算中间节点的算法        key=min(nums[high], key);        if(key==nums[mid]){            mSwap(nums[low], nums[mid]);        }        else if(key==nums[high]){            mSwap(nums[low], nums[high]);        }                while(left<right){            while(left<right && key<nums[right]) right--;            nums[left]=nums[right];            while(left<right && nums[left]<=key) left++;            nums[right]=nums[left];        }        nums[left]=key;        myQsort(nums, low, left-1);        myQsort(nums, left+1, high);    }

3. 堆排序：

void adjust(int a[], int idx, int max){//堆调整函数，因为idx的左右两个子树都是大根堆，所以，可以保证每次调整后，整个堆也是大根堆int left=2*idx+1;int right=left+1;int largest=idx;if(left<max && a[left]>a[largest])largest=left;if(right<max && a[right]>a[largest])largest=right;if(largest!=idx){int tmp=a[largest];a[largest]=a[idx];a[idx]=tmp;adjust(a, largest, max);}}//大根堆void heapSort(int a[], int len){for(int i=len/2-1; i>=0; --i){//初始化建堆时从下往上建堆adjust(a, i, len);}int tmp;for(int i=len-1; i>0; --i){//之后的调整都是从上往下建堆tmp=a[i];//每次都是将根节点放到最后一个位置a[i]=a[0];a[0]=tmp;adjust(a, 0, i);}}

另一种写法：

void swap(int &a, int &b){int tmp=a;a=b;b=tmp;}//大根堆void createHeap(int a[], int len){int bigest;for(int i=len/2; i>=0; i--){bigest=i;if(2*i<len){if(a[2*i]>a[i])bigest=2*i;}if(2*i+1<len){if(a[2*i+1]>a[bigest])bigest=2*i+1;}if(bigest==i)continue;else{swap(a[bigest], a[i]);}}}//堆调整void adjustHeap(int a[], int len){int idx=0;int bigest;while(2*idx<len){bigest=idx;if(a[2*idx]>a[idx])bigest=2*idx;if(2*idx+1<len && a[2*idx+1]>a[bigest])bigest=2*idx+1;if(bigest==idx)break;swap(a[bigest], a[idx]);idx=bigest;}}//堆排序void sortHeap(int a[], int len){createHeap(a, len);for(int i=len-1; i>=0; i--){swap(a[i], a[0]);adjustHeap(a, i);}}

一位大神的总结：

各种排序算法：http://blog.csdn.net/whuslei/article/details/6442755