Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.
For example,
Given n = 3,
You should return the following matrix:
[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ] ]
Have you met this question in a real interview?
Solution:
1 public class Solution { 2 public int[][] generateMatrix(int n) { 3 int[][] matrix = new int[n][n]; 4 5 int[] x = new int[]{0,1,0,-1}; 6 int[] y = new int[]{1,0,-1,0}; 7 int direction = 0; 8 int curX = 0, curY=0; 9 int rowStart = 0, rowEnd = n-1, colStart=0, colEnd=n-1; 10 int len = n*n; 11 12 for (int i=0;i<len;i++){ 13 matrix[curX][curY]=i+1; 14 int nextX = curX+x[direction]; 15 int nextY = curY+y[direction]; 16 //Determin the availability of next point. 17 if (nextX>rowEnd || nextX<rowStart || nextY>colEnd || nextY<colStart){ 18 direction = (direction+1)%4; 19 nextX = curX+x[direction]; 20 nextY = curY+y[direction]; 21 //Update the availability of rows and cols according the direction change. 22 if (direction==1) rowStart++; 23 if (direction==2) colEnd--; 24 if (direction==3) rowEnd--; 25 if (direction==0) colStart++; 26 } 27 curX = nextX; 28 curY = nextY; 29 } 30 31 return matrix; 32 33 } 34 }