leetcode

Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,

Given the following matrix:

[ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ]]

You should return [1,2,3,6,9,8,7,4,5].

Solution:

  public List<Integer> spiralOrder(int[][] matrix) {    List<Integer> result = new ArrayList<Integer>();    if (matrix.length == 0) {      return result;    }    int rowBegin = 0;    int rowEnd = matrix.length - 1;    int colBegin = 0;    int colEnd = matrix[0].length - 1;    while (rowBegin <= rowEnd && colBegin <= colEnd) {      for (int j = colBegin; j <= colEnd; j++) {        result.add(matrix[rowBegin][j]);      }      rowBegin++;      for (int j = rowBegin; j <= rowEnd; j++) {        result.add(matrix[j][colEnd]);      }      colEnd--;      if (rowBegin <= rowEnd) {        for (int j = colEnd; j >= colBegin; j--) {          result.add(matrix[rowEnd][j]);        }      }      rowEnd--;      if (colBegin <= colEnd) {        for (int j = rowEnd; j >= rowBegin; j--) {          result.add(matrix[j][colBegin]);        }      }      colBegin++;    }    return result;  }