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public class SpiralMatrixII {
public int[][] generateMatrix(int n) {
if (n < 0) {
return null;
}
int[][] matrix = new int[n][n];
if (n == 0) {
return matrix;
}
int val = 1;
int x = 0;
int y = 0;
int w = n;
while (w > 0) {
for (int i = 0; i < w - 1; i++) {
matrix[x][y++] = val++;
}
for (int i = 0; i < w - 1; i++) {
matrix[x++][y] = val++;
}
for (int i = 0; i < w - 1; i++) {
matrix[x][y--] = val++;
}
for (int i = 0; i < w - 1; i++) {
matrix[x--][y] = val++;
}
w = w - 2;
x++;
y++;
}
if (n % 2 == 1) {
matrix[n / 2][n / 2] = val;
}
return matrix;
}
}
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