Week 8 Lab Exercise Solutions

ex1.cpp

/*
This code is based on the first solution I posted for exercise 4 from Week 6.  I placed a MODIFIED comment anywhere I changed the code. 
*/

#include <iostream>
#include <vector>

using namespace std;

vector<string> extract_bold(string);
void print_vec(vector<string>&);

int main() {
  string test1 = "To <b>succeed</b> in <b>life</b> one must be <b>bold</b>!";
  vector<string> results = extract_bold(test1);
  print_vec(results);

  return 0;
}

// print function to print out the contents of a vector
void print_vec(vector<string> & v) {
  for (int i = 0; i < v.size(); ++i)
    cout << v.at(i) << endl;
}

vector<string> extract_bold(string htmlText) {
  // these tags and their lengths will never change, so we'll make them const
  const string OPEN_TAG = "<b>";
  const int OPEN_LENGTH = OPEN_TAG.size();
  const string CLOSE_TAG = "</b>";
  const int CLOSE_LENGTH = CLOSE_TAG.size();

  // this vector will hold our results 
  vector<string> results; // MODIFIED
  
  // this is where we'll start searching for the next <b> tag
  int findStartIndex = 0;
  // we'll keep searching so long as there are more <b> tags in the string 
  while (htmlText.find(OPEN_TAG, findStartIndex) != -1) {
    // find the beginning and end of our next result 
    int beginIndex = htmlText.find(OPEN_TAG, findStartIndex) + OPEN_LENGTH;
    int endIndex = htmlText.find(CLOSE_TAG, findStartIndex);

    // substr expects a length, so we'll calculate the length of our next result
    int length = endIndex - beginIndex;

    // extract the next result using substring
    string nextResult = htmlText.substr(beginIndex, length);

    // push the next result onto the end of the results vector
    results.push_back(nextResult); // MODIFIED

    // our new starting search index is after the </b> tag
    findStartIndex = endIndex + CLOSE_LENGTH;
  }

  // MODIFIED

  // return the answer
  return results;
}

ex2.cpp

#include <iostream>
#include <vector>

using namespace std;

bool isOpeningBrace(char);
bool isClosingBrace(char);
bool braceTypeMatches(char, char);
bool bracesMatch(string);

int main() {
  cout << "Enter a string: ";
  string input;
  cin >> input;

  if (bracesMatch(input)) 
    cout << "All braces match" << endl;
  else 
    cout << "Braces are mismatched." << endl;

  return 0;
}

bool isOpeningBrace(char c) {
  return c == '{' || c == '(' || c == '[';
}

bool isClosingBrace(char c) {
  return c == '}' || c == ')' || c == ']';
}

bool braceTypeMatches(char open, char closed) {
  if (open == '{')
    return closed == '}';
  else if (open == '(') 
    return closed == ')';
  else if (open == '[') 
    return closed == ']';
  else
    return false;
}

bool bracesMatch(string s) {
  // create a stack to hold the opening braces 
  vector<char> bracesStack; 

  // iterate over every character of s 
  for (int i = 0; i < s.size(); ++i) {
    // extract the next character 
    char c = s.at(i);

    if (isOpeningBrace(c)) 
      // if the character is an opening brace, push it on the stack 
      bracesStack.push_back(c);
    else if (isClosingBrace(c)) { 
      if (s.size() == 0) 
	return false; // no more opening braces, so this must be a mismatch 
      else {
	// if this closing brace doesn't match the last opening one, there's a mismatch 
	if (!braceTypeMatches(bracesStack.at(bracesStack.size() - 1), c)) 
	  return false;
	// if the brace does match, pop the last one off of the stack 
	bracesStack.pop_back();
      }	
    }
  }

  // if the stack isn't empty at this point, there's a mismatch 
  return bracesStack.size() == 0; 
}

ex3.cpp

#include <iostream>
#include <vector>

using namespace std;

void sort_vec(vector<int>&);
void print_vec(vector<int>&);

int main() {
  vector<int> v;
  v.push_back(3);
  v.push_back(1);
  v.push_back(4);
  v.push_back(1);
  v.push_back(5);
  v.push_back(9);
  v.push_back(2);
  v.push_back(6);
  v.push_back(5);
  v.push_back(3);

  print_vec(v);
  cout << endl;
  sort_vec(v);
  print_vec(v);

  return 0;
}

void print_vec(vector<int> & v) {
  for (int i = 0; i < v.size(); ++i)
    cout << v.at(i) << " ";
}

void sort_vec(vector<int> & v) {
  for (int i = 0; i < v.size(); ++i) {
    for (int j = 0; j < v.size() - 1; ++j) {
      if (v.at(j) > v.at(j + 1)) {
	int temp = v.at(j);
	v.at(j) = v.at(j + 1);
	v.at(j + 1) = temp;
      }
    }
  }
}