PROBLEM DESCRIPTION
Given an integer A, generate a square matrix filled with elements from 1 to A^2 in spiral order and return the generated square matrix.
SOLUTION
Mark the startRow, endRow, startColumn and endColumn. Then, start iterated over the perimeter in the order: top row -> right column -> bottom row -> left column. Once this is covered, update startRow -> startRow++, endRow -> endRow–, startColumn -> startColumn++ and endColumn -> endColumn– for the next perimeter.
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public class Solution {
public int[][] generateMatrix(int A) {
int n = A;
int[][] matrix = new int[n][n];
int startRow = 0;
int endRow = n-1;
int startColumn = 0;
int endColumn = n-1;
int nextVal = 1;
while(startRow <= endRow && startColumn <= endColumn){
//top
for(int i=startColumn; i<=endColumn; i++){
matrix[startRow][i] = nextVal;
nextVal++;
}
//right
for(int i=startRow+1; i<=endRow; i++){
matrix[i][endColumn] = nextVal;
nextVal++;
}
//bottom
for(int i=endColumn-1; i>=startColumn; i--){
matrix[endRow][i] = nextVal;
nextVal++;
}
//left
for(int i=endRow-1; i>=startRow+1; i--){
matrix[i][startColumn] = nextVal;
nextVal++;
}
startRow++;
startColumn++;
endRow--;
endColumn--;
}
return matrix;
}
}