Exercises

Exercises 14.11 Exercises

Note 14.11.1.

When you fail a CHECK the vector will not automatically be displayed. Each problem declares a print function you can use to help debug your code.

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1.

Write code for the function additiveInverse. It should take the 2D matrix given and change it into its additive inverse by multiplying each value in the matrix by -1.

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2.

Write the function vector<vector<int>> create(int rows, int cols);. It should return a 2D vector of integers that is the correct dimensions. All the values should be 0

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Hint.

This should only take 1 or 2 lines of code and should not require any loops. Refer back to the first page in the chapter for an example.

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3.

Complete the function maxValue that returns the largest value from a 2D vector of integers.

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The logic should be the same as finding the maximum value in a 1D vector, you just multiple loops.

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4.

Complete the function diagonalAdder that adds up the numbers on the diagonal (from upper left to lower right) of a 2D vector. You can assume the vector is “square” - it has the same number of rows as columns. For example, in this matrix:

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1 2 3
4 5 6
7 8 9

The diagonal is 1, 5, 9. Adding those up should result in 15.

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Hint 1.

What is true of the row and column number for all elements on the diagonal?

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Hint 2.

You should only need one loop to do this.

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5.

Complete the function revDiagonalAdder that adds up and returns the numbers on the reverse diagonal (from upper right lower left) of a 2D vector of integers. You can assume the vector is “square” - it has the same number of rows as columns. For example, in this matrix:

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1 2 3
4 5 6
0 8 9

The reverse diagonal is 3, 5, 0. Adding those up should result in 8.

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Hint.

There is a relationship between the row and column number. As the row number increases, the column number decreases. Row 0 uses the last column. Row 1 uses the column before that. Row 2 uses the column before that. The last row uses column 0.

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6.

Complete the function secondRowProduct that computes the product of all of the items in the second row of a 2D vector of integers. Given this data:

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1 2 3
4 5 6
0 8 9

You would return 120 (4 * 5 * 6).

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Tip: When multiplying, you will want to start your accumulator variable with 1 not 0.

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7.

Complete the function mirror. Given a 2D vector of integers:

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1 2 3
4 5 6

It should produce a new vector where the data is mirrored horizontally:

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3 2 1
6 5 4

You may assume that the data is always 2 rows and 3 columns.

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#include <iostream>
#include <vector>
using namespace std;

// Debugging helper
void print(const vector<vector<int>>& matrix) {
  size_t rows = matrix.size();
  size_t cols = matrix[0].size();
  for (size_t i = 0; i < rows; ++i) {
      for (size_t j = 0; j < cols; ++j) {
          cout << matrix.at(i).at(j) << " ";
      }
      cout << endl;
  }
}
^^^!

vector<vector<int>> mirror(const vector<vector<int>>& data) {
    // copy the data so result has the same size
    vector<vector<int>> result = data;
    // add code to modify the result
}
===!
#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
#include "doctest.h"

TEST_CASE("revDiagonalAdder") {
    vector<vector<int>> mirror = {{1,7,3},
                                 {4,5,6}};
    vector<vector<int>> result = {{3,7,1},
                                   {6,5,4}};
    CHECK(mirror(result) == result);

vector<vector<int>> test2 = {{-4,0},
                                 {3,2}};
    vector<vector<int>> result2 = {{0,-4},
                                    {2,3}};
    CHECK(mirror(result2) == result2);
}

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