剑指 Offer 29. 顺时针打印矩阵

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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:

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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：

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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]

提示：

  • 0 <= matrix.length <= 100
  • 0 <= matrix[i].length <= 100

解法

解法一：

JAVA

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public int[] spiralOrder(int[][] matrix) {
       int row = matrix.length;
       if (row == 0) {
           return new int[0];
       }
       int col = matrix[0].length;
       int[] res = new int[row * col];
       int idx = 0;
       int left = 0, top = 0, right = col - 1, bottom = row - 1;
       while (true) {
           //从左往右走
           for (int i = left; i <= right; i++) {
               res[idx++] = matrix[top][i];
           }
           if (++top > bottom) {
               break;
           }
           //从上往下走
           for (int i = top; i <= bottom; i++) {
               res[idx++] = matrix[i][right];
           }
           if (--right < left) {
               break;
           }
           //从右往左走
           for (int i = right; i >= left; i--) {
               res[idx++] = matrix[bottom][i];
           }
           if (--bottom < top) {
               break;
           }
           //从下往上走
           for (int i = bottom; i >= top; i--) {
               res[idx++] = matrix[i][left];
           }
           if (++left > right) {
               break;
           }
       }
       return res;
   }

解法二：

超时

Java

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public int[] spiralOrder(int[][] matrix) {

        if (Objects.isNull(matrix)) {
            return null;
        }
        
        if (0 == matrix.length) {
            return new int[]{};
        }

        int[][] directions = new int[4][2];
        directions[0] = new int[]{0, 1};     // x++;
        directions[1] = new int[]{1, 0};     // y++;
        directions[2] = new int[]{0, -1};     // x--;
        directions[3] = new int[]{-1, 0};     // y--

        int[] result = new int[matrix.length * matrix[0].length];
        int index = 0;
        Set<String> visited = new HashSet<>(result.length);
        int row = matrix.length;
        int col = matrix[0].length;
        int directionIndex = 0;
        int r = 0;
        int c = 0;
        while (index < result.length) {
            String p = r + "_" + c;
            if (visited.contains(p)) {
                continue;
            }

            result[index++] = matrix[r][c];

            if (directionIndex == 0 && (c + 1) == col) {
                // 转向
                directionIndex = (directionIndex + 1) % 4;
            } else if (directionIndex == 1 && (r + 1) == row) {
                // 转向
                directionIndex = (directionIndex + 1) % 4;
            } else if (directionIndex == 2 && (c == 0 || visited.contains(p))) {
                // 转向
                directionIndex = (directionIndex + 1) % 4;
            } else if (directionIndex == 3 && (r == 0 || visited.contains((r - 1) + "_" + c))) {
                // 转向
                directionIndex = 0;
            }
            r += directions[directionIndex][0];
            c += directions[directionIndex][1];
            visited.add(p);
        }
        return result;
    }
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