剑指 Offer 29. 顺时针打印矩阵

题目

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字。

 

示例 1：

输入：matrix = [[1,2,3],[4,5,6],[7,8,9]]
输出：[1,2,3,6,9,8,7,4,5]
示例 2：

输入：matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
输出：[1,2,3,4,8,12,11,10,9,5,6,7]
 

限制：
0 <= matrix.length <= 100
0 <= matrix[i].length <= 100

思路

定义四个指针，分别为top，right、bottom、left，能够确定四个角的位置，然后逐层遍历

每次打印完一层后都要判断数组是否发生越界（已经不用打印了）

实现

通过定义的四个变量来判断是否越界

private static class Solution {
    public int[] spiralOrder(int[][] matrix) {
        if (matrix.length == 0) {
            return new int[0];
        }
        int top = 0, right = matrix[0].length - 1, bottom = matrix.length - 1, left = 0;
        int[] result = new int[matrix.length * matrix[0].length];
        int index = 0;
        while (true) {
            // 横向从左向右打印
            for (int row = left; row <= right; row++) {
                result[index++] = matrix[top][row];
            }
            if (++top > bottom) {
                break;
            }

            // 竖向从上到下
            for (int col = top; col <= bottom; col++) {
                result[index++] = matrix[col][right];
            }
            if (--right < left) {
                break;
            }
            //横向从右向左
            for (int row = right; row >= left; row--) {
                result[index++] = matrix[bottom][row];
            }
            if (--bottom < top) {
                break;
            }
            //竖向从下到上
            for (int col = bottom; col >= top; col--) {
                result[index++] = matrix[col][left];
            }
            if (++left > right) {
                break;
            }

        }

        return result;
    }
}

通过数组的值是否满，判断是否越界

private static class Solution2 {
    public int[] spiralOrder(int[][] matrix) {
        if (matrix.length == 0) {
            return new int[0];
        }
        int top = 0, right = matrix[0].length - 1, bottom = matrix.length - 1, left = 0;
        int size = matrix.length * matrix[0].length;
        int[] result = new int[matrix.length * matrix[0].length];
        int index = 0;
        while (true) {
            // 横向从左向右打印
            for (int row = left; row <= right; row++) {
                result[index++] = matrix[top][row];
            }
            top++;
            if (index >= size) {
                break;
            }
            // 竖向从上到下
            for (int col = top; col <= bottom; col++) {
                result[index++] = matrix[col][right];
            }
            right--;
            if (index >= size) {
                break;
            }
            //横向从右向左
            for (int row = right; row >= left; row--) {
                result[index++] = matrix[bottom][row];
            }
            bottom--;
            if (index >= size) {
                break;
            }
            //竖向从下到上
            for (int col = bottom; col >= top; col--) {
                result[index++] = matrix[col][left];
            }
            left++;
            if (index >= size) {
                break;
            }

        }

        return result;
    }
}