归并排序(merge sort)的一个基于模板的实现

来源：互联网发布：php header 编辑：程序博客网时间：2024/05/13 05:21

问题描述：

归并排序分治思想（divide and conquer）在排序中的具体应用，它的时间复杂度为O(NlgN)。问题和实现的详细描述

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代码实现：

#ifndef _MERGE_SORT_H_#define _MERGE_SORT_H_#include <assert.h>#include <iostream>#include <algorithm>#include <functional>#define  MAXLEN  65535/** implement merge for result sorted**/template<class T>void Merge( T item[], int left, int mid, int right ){static T auxItem[MAXLEN];int i;for( i = mid + 1; i > left; i-- ){auxItem[i - 1] = item[i - 1];}int j;for( j = mid; j < right; j++ ){auxItem[right + mid - j] = item[j + 1];}for( int k = left; k <= right; k++ ){if( auxItem[i] < auxItem[j] ){item[k] = auxItem[i++];}else{item[k] = auxItem[j--];}}}/** the implementation of merge sort**/template<class T>void MergeSort( T item[], int left, int right ){if( left >= right )return;int mid = left + ((right - left) >> 1);MergeSort( item, left, mid );MergeSort( item, mid + 1, right );Merge( item, left, mid, right );}/** Implement  merge for sequence sorted**/template<class T>void MergeAB( T c[], T a[], int n, T b[], int m ){for( int i = 0, j = 0, k = 0, k < m + n; k++ ){if( n == i ){c[k] = b[j++];continue;}if( m == j ){c[k] = a[i++];continue;}c[k] = (a[i] < b[j]) ? a[i++] : b[j++];}}/** the implementation of merge sort**/template<class T>void MergeSortBU( T item[], int left, int right ){for( int m = 1; m <= right - left; m = m + m ){for( int i = left; i <= right - m; i += m + m ){Merge( item, i, i + m - 1, min( i + m + m - 1, right) );}}}/** Test interface**/void TestMergeSort(){int arr[] = {11, 2, 4, 32, 43, 44, 74, 21, 111, 1111, 999, 77, 33, 22, 11111, 66, 88, 38, 386};int len = sizeof(arr)/sizeof(arr[0]);MergeSort( arr, 0, len - 1 );for( int i = 0; i < len; i++ ){std::cout << arr[i] << " ";}std::cout << std::endl;//test another implementationint length = 100;int* item = new int[length];assert( item );for( int i = 0; i < length; i++ ){item[i] = i;}std::random_shuffle( item, item + length );MergeSortBU( item, 0, length - 1 );for( int i = 0; i < length; i++ ){if( !(i % 10) && i ){std::cout << std::endl;}std::cout << item[i] << " ";}delete [] item;}#endif

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