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题目地址：

Given an integer n, generate a square matrix filled with elements from 1 to $n^2$ in spiral order.

For example,

You should return the following matrix:

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

题目叫螺旋矩阵，一看示例就明白是什么意思，这种题目的大致思想就是往矩阵里填数字，然后再输出，关键点就是控制好方向和边界就行了。

public class SpiralMatrixII {
       public static int[][] generateMatrix(int n) {        int[][] result = new int[n][n];        int k = 1;        int sqrN = n * n;        boolean goLeft = true;        boolean goDown = false;        boolean goRight = false;        boolean goUp = false;        int i = 0;        int j = 0;        int block = n - 1;        while (k <= sqrN) {            if (goLeft) {                if (j < block) {                    result[i][j] = k;                    j++;                } else if (j == block) {                    //到达边界则修改方向                    result[i][j] = k;                    goLeft = false;                    goDown = true;                    i++;                }            } else if (goDown) {                if (i < block) {                    result[i][j] = k;                    i++;                } else if (i == block) {                    result[i][j] = k;                    goDown = false;                    goRight = true;                    j--;                }            } else if (goRight) {                if (j > n - 1 - block) {                    result[i][j] = k;                    j--;                } else if (j == n - 1 - block) {                    result[i][j] = k;                    goRight = false;                    goUp = true;                    block--;                    i--;                }            } else if (goUp) {                if (i > n - 1 - block) {                    result[i][j] = k;                    i--;                } else if (i == n - 1 - block) {                    result[i][j] = k;                    goUp = false;                    goLeft = true;                    j++;                }            }            k++;        }        return result;    }    public static void print2DArray(int[][] arr) {        for (int i = 0; i < arr.length; i++) {            System.out.print("[");            for (int j = 0; j < arr[i].length; j++) {                System.out.print(arr[i][j] + " ");            }            System.out.println("]");        }    }    public static void main(String[] args) {        print2DArray(generateMatrix(6));    }}

以上算法时间复杂度为： O($n^2$)

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