package leetcode_1To300;

/**
 * 本代码来自 Cspiration，由 @Cspiration 提供
 * 题目来源：http://leetcode.com
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 * - 节省刷题时间，效率提高2-3倍，初学者轻松一天10题，入门者轻松一天20题
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 * - 版权所有，转发请注明出处
 */
public class _59_SpiralMatrixII {

    /**
     * 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 ]
     ]

     time : O(n)     n : 总元素个数
     space : O(n)

     * @param n
     * @return
     */

    public int[][] generateMatrix(int n) {

        int[][] matrix = new int[n][n];
        int rowBegin = 0;
        int rowEnd = n - 1;
        int colBegin = 0;
        int colEnd = n - 1;
        int num = 1;

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

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

            for (int i = colEnd; i >= colBegin; i--) {
                matrix[rowEnd][i] = num++;
            }
            rowEnd--;

            for (int i = rowEnd; i >= rowBegin; i--) {
                matrix[i][colBegin] = num++;
            }
            colBegin++;
        }
        return matrix;
    }
}