_59.java

package com.fishercoder.solutions;

/**
 * 59. Spiral Matrix II
 *
 * 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 ]
 ]
 */
public class _59 {

  public static class Solution1 {
    /**credit: https://leetcode.com/problems/spiral-matrix-ii/discuss/22289/My-Super-Simple-Solution.-Can-be-used-for-both-Spiral-Matrix-I-and-II/21907*/
    public int[][] generateMatrix(int n) {
      int[][] matrix = new int[n][n];
      if (n == 0) {
        return matrix;
      }
      int value = 1;
      int top = 0;
      int bottom = n - 1;
      int left = 0;
      int right = n - 1;
      while (left <= right && top <= bottom) {
        for (int j = left; j <= right; j++) {
          matrix[top][j] = value++;
        }
        top++;
        for (int i = top; i <= bottom; i++) {
          matrix[i][right] = value++;
        }
        right--;
        for (int j = right; j >= left; j--) {
          matrix[bottom][j] = value++;
        }
        bottom--;
        for (int i = bottom; i >= top; i--) {
          matrix[i][left] = value++;
        }
        left++;
      }
      return matrix;
    }
  }
}