cpp/linkedlists/monkey_delstart Source

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Description
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Create a member function <tt>string delStart()</tt>
that deletes the first item in the list, and returns the
<tt>string</tt> it contained (its <tt>name</tt>).
<p>If the list is empty, return an empty string (<tt>""</tt>).
<p>Remember to deallocate the item removed from the list!

Epilogue
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Remarks
Comments, history, license, etc.

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Engine
Choices
json list of string, bool pairs
e.g. [["good", true], ["bad", false]]

Correct answer
Template / Reference solution

Template / Reference solution

\hide[
#include <iostream>
#include <string>
using namespace std;

// structure of items in list
struct Node {
Node* next; // each node knows "next" node
string name; // and stores a value
Node(string initialName); // constructor for nodes
};

Node::Node(string initialName) {name = initialName; next = NULL;}

class MonkeyChain {
public:
MonkeyChain();
void threeKongs();
void printAll();
void addStart(string newName);
bool isEmpty();
int size();
string delStart();
private:
Node* first;
};

MonkeyChain::MonkeyChain() {first = NULL;}

// a demo to create a length-3 list
void MonkeyChain::threeKongs() {
first = new Node("DK Sr.");
first->next = new Node("DK");
first->next->next = new Node("DK Jr.");
}

// we'll provide a working copy of printAll for you
void MonkeyChain::printAll() {
// one possible approach: use a while loop
Node* current = first; // start at beginning

// if current isn't past the last node,
while (current != NULL) {
// print current node's name; then repeat loop w/next one
cout << current->name << endl;
current = current->next;
}
}

// add a new node, containing this name, at the start of the list
void MonkeyChain::addStart(string newName) {
Node* newFirst = new Node(newName);
Node* oldFirst = first;
first = newFirst;
first->next = oldFirst;
// there's also a slightly trickier 2-line solution
}

// add a new node, containing this name, at the start of the list
bool MonkeyChain::isEmpty() {
return first == NULL;
}

int MonkeyChain::size() {
int count = 0;
Node* loc = first;
while (loc != NULL) {
count++;
loc = loc->next;
}
return count;
}
]\

string MonkeyChain::delStart() {
// is it empty?
if (\[first == NULL]\) {
return "";
}
else {
\[
string result = first->name;
Node* newFirst = first->next;
delete first;
first = newFirst;
return result;
]\
}
}

int main() {
MonkeyChain mc;
mc.threeKongs();
cout << "Deleted: " << mc.delStart() << endl;
mc.printAll(); cout << endl;
cout << "Deleted: " << mc.delStart() << endl;
mc.printAll(); cout << endl;
cout << "Deleted: " << mc.delStart() << endl;
cout << boolalpha << mc.isEmpty() << endl;

// deleting from empty should do nothing:
cout << "Deleted: " << mc.delStart() << endl;
cout << boolalpha << mc.isEmpty() << endl;

// test your deallocation
for (int i=0; i<1000000; i++) {
mc.addStart("A");
mc.addStart("B");
mc.delStart();
mc.delStart();
}
}

Java test suite
See manual

C++ test suite
json list of stdin/args tests
e.g. [{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]
to just run once with no input use [{}]

[
{}
]

C++ test suite
See manual

Forbidden substrings
json list of strings
e.g. ["for","while"]

remove
Solution visibility remove
Java imports
json list of importables
e.g. ["java.util.*"]

remove
Override Java classname
else defaults to
websheet name
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Dependent on other websheets?
json list of websheet names in this folder
e.g. ["DataStructure"]

remove
Is example?
i.e., just a demo
remove
Add compiler flag(s)
json list of flags
e.g. ["-Wno-unused-variable"]

remove
Remove default compiler flag(s)
json list of flags
see default_cppflags
e.g. ["-Wno-write-strings"]

remove

Property	Value
Description html markup shown to student	Create a member function <tt>string delStart()</tt> that deletes the first item in the list, and returns the <tt>string</tt> it contained (its <tt>name</tt>). <p>If the list is empty, return an empty string (<tt>""</tt>). <p>Remember to deallocate the item removed from the list!
Epilogue html markup shown when solved	remove
Public permissions	remove
Remarks Comments, history, license, etc.	remove
Engine
Choices json list of string, bool pairs e.g. `[["good", true], ["bad", false]]`
Correct answer
Template / Reference solution
Template / Reference solution	\hide[ #include <iostream> #include <string> using namespace std; // structure of items in list struct Node { Node* next; // each node knows "next" node string name; // and stores a value Node(string initialName); // constructor for nodes }; Node::Node(string initialName) {name = initialName; next = NULL;} class MonkeyChain { public: MonkeyChain(); void threeKongs(); void printAll(); void addStart(string newName); bool isEmpty(); int size(); string delStart(); private: Node* first; }; MonkeyChain::MonkeyChain() {first = NULL;} // a demo to create a length-3 list void MonkeyChain::threeKongs() { first = new Node("DK Sr."); first->next = new Node("DK"); first->next->next = new Node("DK Jr."); } // we'll provide a working copy of printAll for you void MonkeyChain::printAll() { // one possible approach: use a while loop Node* current = first; // start at beginning // if current isn't past the last node, while (current != NULL) { // print current node's name; then repeat loop w/next one cout << current->name << endl; current = current->next; } } // add a new node, containing this name, at the start of the list void MonkeyChain::addStart(string newName) { Node* newFirst = new Node(newName); Node* oldFirst = first; first = newFirst; first->next = oldFirst; // there's also a slightly trickier 2-line solution } // add a new node, containing this name, at the start of the list bool MonkeyChain::isEmpty() { return first == NULL; } int MonkeyChain::size() { int count = 0; Node* loc = first; while (loc != NULL) { count++; loc = loc->next; } return count; } ]\ string MonkeyChain::delStart() { // is it empty? if (\[first == NULL]\) { return ""; } else { \[ string result = first->name; Node* newFirst = first->next; delete first; first = newFirst; return result; ]\ } } int main() { MonkeyChain mc; mc.threeKongs(); cout << "Deleted: " << mc.delStart() << endl; mc.printAll(); cout << endl; cout << "Deleted: " << mc.delStart() << endl; mc.printAll(); cout << endl; cout << "Deleted: " << mc.delStart() << endl; cout << boolalpha << mc.isEmpty() << endl; // deleting from empty should do nothing: cout << "Deleted: " << mc.delStart() << endl; cout << boolalpha << mc.isEmpty() << endl; // test your deallocation for (int i=0; i<1000000; i++) { mc.addStart("A"); mc.addStart("B"); mc.delStart(); mc.delStart(); } }
Java test suite See manual
C++ test suite json list of stdin/args tests e.g. `[{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]` to just run once with no input use `[{}]`	[ {} ]
C++ test suite See manual
Forbidden substrings json list of strings e.g. `["for","while"]`	remove
Solution visibility	remove
Java imports json list of importables e.g. `["java.util.*"]`	remove
Override Java classname else defaults to websheet name	remove
Dependent on other websheets? json list of websheet names in this folder e.g. `["DataStructure"]`	remove
Is example? i.e., just a demo	remove
Add compiler flag(s) json list of flags e.g. `["-Wno-unused-variable"]`	remove
Remove default compiler flag(s) json list of flags see default_cppflags e.g. `["-Wno-write-strings"]`	remove

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