leetcode59. Spiral Matrix II

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本文介绍了一种生成螺旋矩阵的方法，对于给定的整数n，可以生成一个n×n的螺旋矩阵，矩阵中填充从1到n²的元素。通过四个指针维护矩阵的边界，并按螺旋顺序填充数字。

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 ]
]

解法

同leetcode54. Spiral Matrix，维护四个指针。

public class Solution {
    public int[][] generateMatrix(int n) {
        // Declaration
        int[][] matrix = new int[n][n];

        // Edge Case
        if (n == 0) {
            return matrix;
        }

        // Normal Case
        int rowBegin = 0;
        int rowEnd = n - 1;
        int colBegin = 0;
        int colEnd = n - 1;
        int num = 1; //change

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

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

            for (int i = colEnd; i >= colBegin; i--) {
                if (rowBegin <= rowEnd)
                    matrix[rowEnd][i] = num++; //change
            }
            rowEnd--;

            for (int i = rowEnd; i >= rowBegin; i--) {
                if (colBegin <= colEnd)
                    matrix[i][colBegin] = num++; //change
            }
            colBegin++;
        }

        return matrix;
    }
}