Traversing 2D Arrays Practice

Part of 2D Array.

Practice questions

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Sample questions

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Sample 1difficulty 2/5

int[][] m = {{2, 3}, {4, 5}};
int product = 1;
for (int[] row : m) {
    for (int x : row) {
        product *= x;
    }
}
System.out.println(product);

What is printed?

A
$120$
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B
$60$
C
$100$
D
$14$

Why

2 * 3 * 4 * 5 = 120.

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Sample 2difficulty 3/5

public static int run() {
    int[][] m = {{1,2,3},{4,5,6}};
    int s = 0;
    for (int[] row : m) {
        for (int v : row) {
            if (v % 2 == 1) s += v;
        }
    }
    return s;
}
// Call: System.out.println(run());

What is printed?

A
$12$
B
$21$
C
$6$
D
$9$
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Why

Odd values: 1, 3, 5. Sum = 9.

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Sample 3difficulty 3/5

public static int run() {
    int[][] g = new int[3][3];
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++)
            g[i][j] = i * 3 + j;
    g[1][1] = g[0][2] + g[2][0];
    return g[1][1];
}
// Call: System.out.println(run());

What is printed?

A
$4$
B
$8$
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C
$10$
D
$6$

Why

g[0][2] = 0 <em> 3+2 = 2. g[2][0] = 2 </em> 3+0 = 6. g[1][1] = 2 + 6 = 8.

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Sample 4difficulty 3/5
```
for (int r = 0; r <= grid.length; r++) {
    for (int c = 0; c < grid[0].length; c++) {
        grid[r][c] = 0;
    }
}
```
$Which fix corrects the bounds error?$
- A
  $Change r <= grid.length to r < grid.length$
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- B
  $Swap rows and columns$
- C
  $Use grid[r-1][c]$
- D
  $Change c < grid[0].length to c <= grid[0].length$
Why
$Row indices run 0 to grid.length-1. The outer condition must be r < grid.length to avoid an out-of-bounds access.$
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Sample 5difficulty 3/5
```
public static int sum2D(int[][] g) {
    int total = 0;
    for (int r = 0; r < g.length; r++) {
        for (int c = 0; c < /* missing */; c++) {
            total += g[r][c];
        }
    }
    return total;
}
```
$Which expression replaces /* missing */ assuming each row may differ in length?$
- A
  $g[c].length$
- B
  $g[0].length$
- C
  $g.length$
- D
  $g[r].length$
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Why
$For ragged arrays, use the length of the current row g[r].length. g[0].length only works for rectangular grids.$
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