A spiral number pattern is a square matrix in which numbers are arranged in a spiral order. The numbers start from the top-left corner and move right, down, left, and up, repeatedly, until all positions in the matrix are filled.
- After filling each side, the corresponding boundary moves inward.
- The process continues until all matrix cells are filled.
Illustration
Input: n = 4
Output:
1 2 3 4
12 13 14 5
11 16 15 6
10 9 8 7
Here, the numbers are filled in the following order:
Right-> Down-> Left-> Up -> Right -> ...... and keep on repeating the same
Approach
To print the spiral pattern:
- Create an n × n matrix.
- Start from the top-left cell and place numbers from 1 to n × n.
- Move in four directions: right, down, left, and up.
- Change direction whenever the next cell is outside the matrix or has already been filled.
- Continue until all cells contain a number.
- Finally, print the matrix row by row.
public class GFG {
static void printSpiral(int n) {
int[][] matrix = new int[n][n];
int top = 0, bottom = n - 1;
int left = 0, right = n - 1;
int num = 1;
while (top <= bottom && left <= right) {
// Left to right
for (int col = left; col <= right; col++) {
matrix[top][col] = num++;
}
top++;
// Top to bottom
for (int row = top; row <= bottom; row++) {
matrix[row][right] = num++;
}
right--;
// Right to left
if (top <= bottom) {
for (int col = right; col >= left; col--) {
matrix[bottom][col] = num++;
}
bottom--;
}
// Bottom to top
if (left <= right) {
for (int row = bottom; row >= top; row--) {
matrix[row][left] = num++;
}
left++;
}
}
// Print matrix
for (int row = 0; row < n; row++) {
for (int col = 0; col < n; col++) {
System.out.print(matrix[row][col] + " ");
}
System.out.println();
}
}
public static void main(String[] args) {
int n = 4;
printSpiral(n);
}
}
Output
1 2 3 4 12 13 14 5 11 16 15 6 10 9 8 7
Explanation: The program uses four boundaries: top, bottom, left, and right. It fills the matrix in four directions—right, down, left, and up—and moves the corresponding boundary inward after each pass until all cells are filled.
