Jagged Arrays

1// Creating jagged arrays - Method 1
2int[][] jagged = new int[3][];    // 3 rows, columns undefined
3
4jagged[0] = new int[4];           // First row: 4 elements
5jagged[1] = new int[2];           // Second row: 2 elements
6jagged[2] = new int[3];           // Third row: 3 elements
7
8// Fill with values
9jagged[0] = new int[]{1, 2, 3, 4};
10jagged[1] = new int[]{5, 6};
11jagged[2] = new int[]{7, 8, 9};
12
13// Method 2: Direct initialization
14int[][] triangle = {
15    {1},
16    {2, 3},
17    {4, 5, 6},
18    {7, 8, 9, 10}
19};

1// Iterating jagged arrays
2int[][] jagged = {
3    {1, 2, 3, 4},
4    {5, 6},
5    {7, 8, 9}
6};
7
8// Safe iteration - check each row's length
9for (int i = 0; i < jagged.length; i++) {
10    System.out.print("Row " + i + ": ");
11    for (int j = 0; j < jagged[i].length; j++) {  // Use jagged[i].length!
12        System.out.print(jagged[i][j] + " ");
13    }
14    System.out.println();
15}
16
17// Enhanced for loop (automatically handles different lengths)
18for (int[] row : jagged) {
19    for (int value : row) {
20        System.out.print(value + " ");
21    }
22    System.out.println();
23}

1// Pascal's Triangle example
2int numRows = 5;
3int[][] pascal = new int[numRows][];
4
5for (int i = 0; i < numRows; i++) {
6    pascal[i] = new int[i + 1];     // Each row has i+1 elements
7    pascal[i][0] = 1;                // First element is 1
8    pascal[i][i] = 1;                // Last element is 1
9    
10    for (int j = 1; j < i; j++) {
11        pascal[i][j] = pascal[i-1][j-1] + pascal[i-1][j];
12    }
13}
14
15// Print Pascal's Triangle
16for (int[] row : pascal) {
17    for (int val : row) {
18        System.out.print(val + " ");
19    }
20    System.out.println();
21}
22/*
231 
241 1 
251 2 1 
261 3 3 1 
271 4 6 4 1 
28*/

1// Practical use case: Student grades
2// Each student may have different number of assignments
3String[] students = {"Alice", "Bob", "Charlie"};
4int[][] grades = {
5    {95, 87, 92, 88},      // Alice: 4 assignments
6    {78, 85},               // Bob: 2 assignments
7    {90, 88, 76, 95, 89}   // Charlie: 5 assignments
8};
9
10// Calculate average for each student
11for (int i = 0; i < students.length; i++) {
12    int sum = 0;
13    for (int grade : grades[i]) {
14        sum += grade;
15    }
16    double avg = (double) sum / grades[i].length;
17    System.out.printf("%s: %.2f (from %d assignments)%n",
18        students[i], avg, grades[i].length);
19}
20
21// Find total elements in jagged array
22int totalElements = 0;
23for (int[] row : grades) {
24    totalElements += row.length;
25}
26System.out.println("Total grades: " + totalElements);