[leetcode]54. Spiral Matrix2生成螺旋数组

import java.util.Arrays;

/**
 * Created by lvhao on 2017/7/6.
 * 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 ]
 ]
 54题螺旋取数的逆过程，生成螺旋数组，思路是一样的
 */
public class Q59SpiralMatrix2 {
    public static void main(String[] args) {
        for (int[] num : generateMatrix(5))
            System.out.println(Arrays.toString(num));
    }
    public static int[][] generateMatrix(int n) {
        int[][] res = new int[n][n];
        //特殊情况
        if (n == 0)
            return res;
        int[] nums = new int[n*n];
        //设置cur记录当前取到哪个数了
        int cur = 0;
        //生成原始数据
        for (int i = 1; i <= (n*n); i++) {
            nums[i-1] = i;
        }
        //外循环是层数
        for (int i = 0; i < n / 2; i++) {
            //里边四个循环分别生成上右下左四边，记得每次取完数cur+1
            //上边
            for (int j = 0; j < n - (i * 2) - 1; j++) {
                res[i][i+j] = nums[cur];
                cur++;
            }
            //右边
            for (int j = 0; j < n - (i * 2) - 1; j++) {
                res[i+j][n-i-1] = nums[cur];
                cur++;
            }
            //下边
            for (int j = 0; j < n - (i * 2) - 1; j++) {
                res[n-1-i][n-1-i-j] = nums[cur];
                cur++;
            }
            //左边
            for (int j = 0; j < n - (i * 2) - 1; j++) {
                res[n-1-i-j][i] = nums[cur];
                cur++;
            }
        }
        //n是奇数时最后一个数循环不到，单独考虑
        if (n%2 != 0)
        {
            res[n/2][n/2] = nums[n*n-1];
        }
        return res;
    }
}