collections-mystery.md

CSE 143

Collections Mystery

Final Study Session

1. Consider the following method:

   public Set<Integer> mystery(int[][] data, int pos, int n) {
   	Set<Integer> result = new TreeSet<Integer>();
   	for (int i = 0; i < n; i++) {
   		for (int j = 0; j < n; j++) {
   			result.add(data[i + pos][j + pos]);
   		}
   	}
   	return result;
   }

   Suppose that a variable called grid has been declared as follows:

   int[][] grid = {{8, 2, 7, 8, 2, 1}, {1, 5, 1, 7, 4, 7},
   				{5, 9, 6, 7, 3, 2}, {7, 8, 7, 7, 7, 9},
   				{4, 2, 6, 9, 2, 3}, {2, 2, 8, 1, 1, 3}};

   which means it will store the following 6-by-6 grid of values:

   8       2       7       8       2       1       
   1       5       1       7       4       7       
   5       9       6       7       3       2       
   7       8       7       7       7       9       
   4       2       6       9       2       3       
   2       2       8       1       1       3  
   

   For each call below, indicate what value is returned. If the method call results in an exception being thrown, write "exception" instead.

   Method Call	Contents of Set Returned
   mystery(grid, 2, 2)
   mystery(grid, 0, 2)
   mystery(grid, 3, 3)

2. Consider the following method:

   public static Map<String, Integer> mystery(String[][] a) {
   	Map<String, Integer> result = new TreeMap<String, Integer>();
   	for (int i = 0; i < a.length; i++) {
   		for (int j = 0; j < a[i].length; j++) {
   			result.put(a[i][j], j);
   		}
   	}
   	return result;
   } 

   In the left-hand column below are specific two-dimensional arrays. Indicate in the right-hand column what values would be stored in the map returned by method mystery if the array in the left-hand column is passed as a parameter to mystery. Recall that maps print in a key=value format. Your answer should display the right keys and values in the right order

   Map	Output
   [["a", "b"], ["c", "d", "e"], ["f"]]
   [["y", "a", "y"], ["b", "r", "e", "a", "k"]]
   [["n", "e", "v", "e", "r"], ["o", "d", "d"], ["o", "r"], ["e", "v", "e", "n"]]

3. Consider the following method:

   public int mystery(int[][] data, int pos) {
   	int sum = 0;
   	for (int i = 0; i < data.length - pos; i++) {
   		sum += data[i][i + pos];
   	}
   	return sum;
   }

   Suppose that a variable called grid has been declared as follows:

   int[][] grid = {{2, 2, 6, 7, 7, 5}, {6, 3, 4, 7, 9, 3},
   				{7, 6, 1, 2, 3, 6}, {9, 3, 6, 6, 9, 4},
   				{3, 1, 8, 8, 2, 7}, {5, 7, 9, 2, 1, 6}};

   which means it will store the following 6-by-6 grid of values:

   2       2       6       7       7       5       
   6       3       4       7       9       3       
   7       6       1       2       3       6       
   9       3       6       6       9       4       
   3       1       8       8       2       7       
   5       7       9       2       1       6       
   

   For each call below, indicate what value is returned. If the method call results in an exception being thrown, write "exception" instead.

   Method Call	Value Returned
   mystery(grid, 5);
   mystery(grid, 3);
   mystery(grid, 1);

4. Consider the following method:

   public void mystery(int[][] data, int pos, int rows, int cols) {
   	for (int i = 0; i < rows; i++) {
   		int sum = 0;
   		for (int j = 0; j < cols; j++) {
   			sum = sum + data[pos + i][pos + j];
   		}
   		System.out.print(sum + " ");
   	}
   	System.out.println();
   }

   Suppose that a variable called grid has been declared as follows:

   int[][] grid = {{4, 6, 8, 8, 2, 1}, {7, 4, 8, 8, 7, 7},
   				{7, 8, 6, 6, 7, 2}, {1, 2, 2, 7, 5, 7},
   				{8, 3, 6, 6, 1, 1}, {9, 7, 9, 6, 6, 1}};

   which means it will store the following 6-by-6 grid of values:

   4       6       8       8       2       1       
   7       4       8       8       7       7       
   7       8       6       6       7       2       
   1       2       2       7       5       7       
   8       3       6       6       1       1       
   9       7       9       6       6       1     
   

   For each call below, indicate what output is produced:

   Method Call	Output Produced
   mystery(grid, 0, 2, 2);
   mystery(grid, 2, 3, 2);
   mystery(grid, 1, 4, 1);