自学排序笔记

 排序算法学习笔记， 看了遍书随便写写，意思到位。

 

#include <algorithm>
#include <list>
#include <vector>
#include <iostream>
#include <string>

void InsertionSort( std::list< std::string > & ls ) ;
void InsertAndKeepOrder( std::list< std::string > &ls, const std::string& str ) ;
void SelectionSort( std::list< std::string > & ls) ;
//void ShellSort( std::list< std::string> &ls ) ;
void QuickSort( std::list< std::string > &ls ) ;
void MergeSort( std::list< std::string > &ls ) ;
void Print( const std::list< std::string > &ls ) ;

int main( int argc, char* argv[] ) {

  std::list< std::string > ls ;
  ls.push_back( "zera" ) ;
  ls.push_back( "b" ) ;
  ls.push_back( "e" ) ;
  ls.push_back( "a" ) ;
  ls.push_back( "f" ) ;
  ls.push_back( "go" ) ;
  ls.push_back( "make" ) ;
  ls.push_back( "hello" ) ;
  ls.push_back( "alalalal" ) ;
  ls.push_back( "sony" ) ;
  ls.push_back( "apple" ) ;
  ls.push_back( "yahoo" ) ;
  ls.push_back( "google" ) ;
  ls.push_back( "microsoft" ) ;

  std::cout << "before sorting: " <<  std::endl ;
  Print( ls ) ;

  // InsertionSort( ls ) ;
  // SelectionSort( ls ) ;
  // ShellSort( ls ) ;
  // std::sort( ls.begin(), ls.end() ) ;
  // QuickSort( ls ) ;
  MergeSort( ls ) ;

  std::cout << "after sorting: " << std::endl ;
  Print( ls ) ;

  return 0 ;
}

void InsertionSort( std::list< std::string > &ls ) {
  std::list< std::string > temp ;
  std::string s ;
  for( std::list< std::string >::iterator it = ls.begin() ; it != ls.end() ; ++it ) {
    s = (*it) ;
    InsertAndKeepOrder( temp, s ) ;
  }
  ls = temp ;
}

void InsertAndKeepOrder( std::list< std::string > &ls, const std::string& str ) {
  std::list< std::string >::iterator it = ls.begin() ;
  while( it != ls.end() && (*it) < str ) {
    ++it ;
  }
  ls.insert( it, str ) ;
}

void SelectionSort( std::list< std::string > &ls ) {
  std::list< std::string>::iterator b = ls.begin() ;
  std::list< std::string>::iterator smallest = ls.begin() ;
  std::string tempSwap ;
  std::list< std::string>::iterator it ;
  while( b != ls.end() ) {
    for( it = b ;  it != ls.end() ; ++it ) {
      if( (*it) < (*smallest) ) {
    smallest = it ;
      }
    }
    //swap
    tempSwap = *b ;
    *b = *smallest ;
    *smallest = tempSwap ;

    smallest = (++b) ;
  }
}

// void ShellSort( std::list< std::string > &ls ) {
//   int step ;
//   std::list< std::string > temp ;
//   unsigned int it ;
//   unsigned int startPoint ;

//   for( step = 5 ; step != -1 ; step -= 2 ) {
//     for( int i = 0 ; i < step ; ++i ) {
//       startPoint = i ;
//       it = startPoint ;
//       while( it < ls.size() ) {
//  temp.push_back( ls[it] ) ;
//  it += step ;
//       }
//       InsertionSort( temp ) ;

//       it = startPoint ;
//       for( unsigned int i = 0 ; i < temp.size() ; ++i ) {
//  ls[ it ] = temp[ i ] ;
//  it += step ;
//       }
//       temp.clear() ;
//     }
//   }
// }

void QuickSort( std::list< std::string > &ls ) {
  if( ls.empty() or ( ls.size() == 1 ) ) {
    return ;
  }
  std::list< std::string> result ;
  std::string temp ;
  std::string pivot = ls.front() ;
  ls.pop_front() ;
  std::list< std::string > subLeft ;
  std::list< std::string > subRight ;
  for( std::list< std::string >::iterator it = ls.begin() ; it != ls.end() ; ++it ) {
    temp = (*it) ;
    if( temp < pivot ) {
      subLeft.push_back( temp ) ;
    }
    else {
      subRight.push_back( temp ) ;
    }
  }
  QuickSort( subLeft ) ;
  QuickSort( subRight ) ;

  //combine together
  result.merge( subLeft ) ;
  result.push_back( pivot ) ;
  result.merge( subRight ) ;
  ls = result ;
}

void MergeSort( std::list< std::string > &ls ) {
  if( ls.empty() or ( ls.size() == 1 ) ) {
    return ;
  }
  std::vector< std::string > l( ls.begin(), ls.end() ) ;
  unsigned int spiltter = l.size() / 2 ;
  std::list< std::string> left ;
  std::list< std::string> right ;
  std::list< std::string> result ;
  std::string temp ;
  //devide
  for( unsigned int i = 0 ; i < l.size() ; ++i ) {
    temp = l[i] ;
    if( i < spiltter ) {
      left.push_back( temp ) ;
    }
    else {
      right.push_back( temp ) ;
    }
  }
  MergeSort( left ) ;
  MergeSort( right ) ;

  //now merge;
  std::list< std::string>::iterator  leftIterator = left.begin() ;
  std::list < std::string>::iterator rightIterator = right.begin() ;
  while( leftIterator != left.end() and rightIterator != right.end() ) {
    if( (*leftIterator) < (*rightIterator ) ) {
      temp = (*leftIterator ) ;
      ++leftIterator ;
    }
    else {
      temp = (*rightIterator) ;
      ++rightIterator ;
    }
    result.push_back( temp ) ;
  }
  if( leftIterator == left.end() ) {
    std::list< std::string > tempList( rightIterator, right.end() ) ;
    result.merge( tempList ) ;
  }
  if( rightIterator == right.end() ) {
    std::list< std::string > tempList( leftIterator, left.end() ) ;
    result.merge( tempList ) ;
  }
  ls = result ;
}

void Print( const std::list< std::string > &ls ) {
  for( std::list< std::string >::const_iterator it = ls.begin() ; it != ls.end() ; ++it ) {
    std::cout << (*it) << std::endl ;
  }
}