Paste_Image.png

My code:

public class Solution {
    public int[][] generateMatrix(int n) {
        if (n < 0)
            return null;
        int[][] result = new int[n][n];
        if (n == 0)
            return result;
                int level = n % 2 + n / 2;
        int count = 1;
        for (int i = 0; i < level; i++) {
            for (int j = i; j < i + n - 2 * i; j++)
                result[i][j] = count++;
            if (n - 2 * i == 1)
                return result;
            for (int j = i + 1; j < i + n - 2 * i; j++)
                result[j][i + n - 2 * i - 1] = count++;
            for (int j = i + n - 2 * i - 2; j >= i; j--)
                result[i + n - 2 * i - 1][j] = count++;
            for (int j = i + n - 2 * i - 2; j > i; j--)
                result[j][i] = count++;
        }
        return result;
    }
    
    public static void main (String[] args) {
        Solution test = new Solution();
        int[][] a = test.generateMatrix(4);
        for (int i = 0; i < a.length; i++) {
            for (int j = 0; j < a[0].length; j++)
                System.out.print(a[i][j] + " ");
            System.out.println();
        }
        
    }
}

My test result:

这道题目和之前的差不多。刚才因为偷懒，写了子函数没改掉，所以运行时间过长。
这道题目，就直接写在主函数的循环里面了，然后那么多for循环基本一笔写成，也基本没什么问题。脑子已经特别清楚了。虽然很累。
题目本身没有任何难度或者任何思想。。。

**
总结： Array, Math
**

Anyway, Good luck, Richardo!

My code:

public class Solution {
    private int counter = 1;
    public int[][] generateMatrix(int n) {
        int[][] ret = new int[n][n];
        if (n <= 0)
            return ret;
        int scanTimes = (n + 1) / 2;
        int beginRow = 0;
        int beginCol = 0;
        for (int i = 0; i < scanTimes; i++) {
            helper(beginRow + i, beginCol + i, n - i * 2, ret);
        }
        return ret;
    }
    
    private void helper(int beginRow, int beginCol, int len, int[][] matrix) {
        if (len == 1) {
            matrix[beginRow][beginCol] = counter;
            return;
        }
        for (int i = beginCol; i < beginCol + len; i++) {
            matrix[beginRow][i] = counter;
            counter++;
        }
        for (int i = beginRow + 1; i < beginRow + len; i++) {
            matrix[i][beginCol + len - 1] = counter;
            counter++;
        }
        for (int i = beginCol + len - 2; i >= beginCol; i--) {
            matrix[beginRow + len - 1][i] = counter;
            counter++;
        }
        for (int i = beginRow + len - 2; i > beginRow; i--) {
            matrix[i][beginCol] = counter;
            counter++;
        }
    }
}

这题目也没什么意思。。。

Anyway, Good luck, Richardo!

My code:

public class Solution {
    public int[][] generateMatrix(int n) {
        if (n < 0) {
            return null;
        }
        
        int[][] matrix = new int[n][n];
        int rowBegin = 0;
        int rowEnd = n - 1;
        int colBegin = 0;
        int colEnd = n - 1;
        int counter = 1;
        while (rowBegin <= rowEnd && colBegin <= colEnd) {
            for (int i = colBegin; i <= colEnd; i++) {
                matrix[rowBegin][i] = counter;
                counter++;
            }
            rowBegin++;
            
            for (int i = rowBegin; i <= rowEnd; i++) {
                matrix[i][colEnd] = counter;
                counter++;
            }
            colEnd--;
            
            if (rowBegin <= rowEnd) {
                for (int i = colEnd; i >= colBegin; i--) {
                    matrix[rowEnd][i] = counter;
                    counter++;
                }
                rowEnd--;
            }
            
            if (colBegin <= colEnd) {
                for (int i = rowEnd; i>= rowBegin; i--) {
                    matrix[i][colBegin] = counter;
                    counter++;
                }
                colBegin++;
            }
        }
        
        return matrix;
    }
}

用之前 Spiral Matrix I 的做法来做，很快很方便。

Anyway, Good luck, Richardo! --- 08/11/2016