算法 简单总结（一）

1） 快速排序

#include <stdio.h>int partition(int *arr,int low,int high){    int pivot=arr[high];    int i=low-1;    int j,tmp;    for(j=low;j<high;++j)        if(arr[j]<pivot){            tmp=arr[++i];            arr[i]=arr[j];            arr[j]=tmp;        }    tmp=arr[i+1];    arr[i+1]=arr[high];    arr[high]=tmp;    return i+1;}void quick_sort(int *arr,int low,int high){    if(low<high){        int mid=partition(arr,low,high);        quick_sort(arr,low,mid-1);        quick_sort(arr,mid+1,high);    }}//testint main(){    int arr[10]={1,4,6,2,5,8,7,6,9,12};    quick_sort(arr,0,9);    int i;    for(i=0;i<10;++i)        printf("%d ",arr[i]);}

2）堆排序

#include <stdio.h>#include <stdio.h>#include <stdlib.h>#define PARENT(i) (i)/2#define LEFT(i) 2*(i)+1#define RIGHT(i) 2*(i+1)void swap(int *a,int *b){*a=*a^*b;  *b=*a^*b;  *a=*a^*b;  }void max_heapify(int *arr,int index,int len){int l=LEFT(index);int r=RIGHT(index);int largest;if(l<len && arr[l]>arr[index])largest=l;elselargest=index;if(r<len && arr[r]>arr[largest])largest=r;if(largest != index){//将最大元素提升，并递归swap(&arr[largest],&arr[index]);max_heapify(arr,largest,len);}}void build_maxheap(int *arr,int len){int i;if(arr==NULL || len<=1)return;for(i=len/2+1;i>=0;--i)max_heapify(arr,i,len);}void heap_sort(int *arr,int len){int i;if(arr==NULL || len<=1)return;build_maxheap(arr,len);for(i=len-1;i>=1;--i){swap(&arr[0],&arr[i]);max_heapify(arr,0,--len);}}int main(){int arr[10]={1,4,6,2,5,8,7,6,9,12};int i;heap_sort(arr,10);for(i=0;i<10;++i)printf("%d ",arr[i]);system("pause");}

3）归并排序

#include <stdio.h>#include <stdlib.h>#define MAX_INT  ~(1<<31)//最大整数//arr[p,q]  arr[q+1,r]void merge(int *arr,int p,int q,int r){if(arr==NULL)    return;int n1=q-p+1;int n2=r-q;int *L=(int*)malloc((n1+1)*sizeof(int));int *R=(int*)malloc((n2+1)*sizeof(int));int i,j;for(i=0;i<n1;++i)L[i]=arr[p+i];for(j=0;j<n2;++j)R[j]=arr[q+j+1];//哨兵元素赋值L[n1]=MAX_INT;R[n2]=MAX_INT;int k;i=0,j=0;for(k=p;k<=r;++k){if(L[i]<=R[j])arr[k]=L[i++];elsearr[k]=R[j++];}free(L);free(R);}void merge_sort(int *arr,int p,int r){if(p<r){int q=(r+p)/2;merge_sort(arr,p,q);//分治merge_sort(arr,q+1,r);merge(arr,p,q,r);//合并结果}}int main(){int arr[8]={32,3,4,5,6,7,9,106};merge_sort(arr,0,7);for (int i=0;i<8;i++){printf("%d ",arr[i]);}system("pause");}

4）二分查找

//算法所操作的区间,是左闭右开区间,还是左闭右闭区间,这个区间,需要在循环初始化,//循环体是否终止的判断中,以及每次修改left,right区间值这三个地方保持一致,否则就可能出错.//二分查找实现一int BinarySearch(int array[], int n, int v){    int left, right, middle;    left = 0, right = n - 1;    while (left <= right)    {        middle = left + (right - left) / 2;        if (array[middle] > v)        {            right = middle - 1;        }        else if (array[middle] < v)        {            left = middle + 1;        }        else        {            return middle;        }    }    return -1;}//二分查找实现二int BinarySearch(int array[], int n, int v){    int left, right, middle;    left = 0, right = n;    while (left < right)    {        middle = left + (right - left) / 2;        if (array[middle] > v)        {            right = middle;        }        else if (array[middle] < v)        {            left = middle + 1;        }        else        {            return middle;        }    }    return -1;}

5）线性查找

//QuickSelect 将第k小的元素放在 a[k-1]  void QuickSelect( int a[], int k, int left, int right ){    int i, j;    int pivot;    if( left + cutoff <= right )    {        pivot = median3( a, left, right );        //取三数中值作为枢纽元，可以很大程度上避免最坏情况        i = left; j = right - 1;        for( ; ; )        {            while( a[ ++i ] < pivot ){ }            while( a[ --j ] > pivot ){ }            if( i < j )                swap( &a[ i ], &a[ j ] );            else                break;        }        //重置枢纽元        swap( &a[ i ], &a[ right - 1 ] );          if( k <= i )            QuickSelect( a, k, left, i - 1 );        else if( k > i + 1 )            QuickSelect( a, k, i + 1, right );    }    else          InsertSort( a + left, right - left + 1 );}