leetcode

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;  }