leetcode - 59.Spiral Matrix II

最新推荐文章于 2019-07-07 11:13:21 发布

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最新推荐文章于 2019-07-07 11:13:21 发布

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本文介绍了一个生成螺旋矩阵的算法，该算法接收一个整数n作为输入，并返回一个n×n的螺旋矩阵。矩阵中填充了从1到n²的元素，按照螺旋顺序排列。

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 ]
]

Solution:

  public int[][] generateMatrix(int n) {
    int[][] result = new int[n][n];
    if (n == 0) {
      return result;
    }

    int rowBegin = 0;
    int rowEnd = n - 1;
    int colBegin = 0;
    int colEnd = n - 1;
    int i = 1;

    while (rowBegin <= rowEnd && colBegin <= colEnd) {
      for (int j = colBegin; j <= colEnd; j++) {
        result[rowBegin][j] = i++;
      }
      rowBegin++;

      for (int j = rowBegin; j <= rowEnd; j++) {
        result[j][colEnd] = i++;
      }
      colEnd--;

      if (rowBegin <= rowEnd) {
        for (int j = colEnd; j >= colBegin; j--) {
          result[rowEnd][j] = i++;
        }
      }
      rowEnd--;

      if (colBegin <= colEnd) {
        for (int j = rowEnd; j >= rowBegin; j--) {
          result[j][colBegin] = i++;
        }
      }
      colBegin++;
    }

    return result;
  }