quickselect.cpp

$*$ Author :

$*$ Pledge :

$*$ Date :

$*$ Description : Implements the quickselect algorithm.

$******************************************************************************/$

#include

#include

#include

#include

using namespace std;

size$\_$t lomuto$\_$partition$($int array$[],$ size$\_$t left, size$\_$t right$)\{$

$//$ TODO

$//$ DO NOT change the function header in any way, otherwise you will lose

points.

return $0$;

$\}$

int quick$\_$select$($int array$[],$ size$\_$t left, size$\_$t right, size$\_$t k$)\{$

$//$ TODO

$//$ DO NOT change the function header in any way, otherwise you will lose

points.

return $0$;

$\}$

int quick$\_$select$($int array$[],$ const size$\_$t length, size$\_$t k$)\{$

return quick$\_$select$($array$,0,$ length $-1,$ k$)$;

$\}$

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

if $($argc $!=2)\{$

cerr $<<$ "Usage: $"<<$ argv$[0]<<""<<$ endl;

return $1$;

$\}$

int k;

istringstream iss;

iss.str$($argv$[1])$;

if $(!($iss $>>$ k$)||$ k $<=0)\{$

cerr $<<$ "Error: Invalid value $\text{'}"<<$ argv$[1]<<"\text{'}$ for k$."<<$ endl;

return $1$;

$\}$

cout $<<$ "Enter sequence of integers, each followed by a space: $"<<$ flush;

int value, index $=0$;

vector values;

string str;

str$.$reserve$(11)$;

char c;

iss.clear$()$;

while $($true$)\{$

c $=$ getchar$()$;

const bool eoln $=$ c $==\text{'}\backslash$r$\text{'}||$ c $==\text{'}$

$\text{'}$;

if $($isspace$($c$)||$ eoln$)\{$

if $($str$.$length$()>0)\{$

iss.str$($str$)$;

if $($iss $>>$ value$)\{$

values.push$\_$back$($value$)$;

$\}$ else $\{$

cerr $<<$ "Error: Non$-$integer value $\text{'}"<<$ str

$<<"\text{'}$ received at index $"<<$ index $<<"."<<$ endl;

return $1$;

$\}$

iss.clear$()$;

$++$index;

$\}$

if $($eoln$)\{$

break;

$\}$

str$.$clear$()$;

$\}$ else $\{$

str $+=$ c;

$\}$

$\}$

int num$\_$values $=$ values.size$()$;

if $($num$\_$values $==0)\{$

cerr $<<$ "Error: Sequence of integers not received." $<<$ endl;

return $1$;

$\}$

$//$ TODO $-$ error checking k against the size of the input

$//$ TODO $-$ call the quick$\_$select function and display the result

return $0$;