JZ-019- clockwise printing matrix

Print matrix clockwise

Title description

Enter a matrix and print out each number in clockwise order from the outside to the inside. For example, if you enter the following 4 X 4

• Matrix: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
• Then print out the numbers 1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10.

topic link : clockwise print matrix

Code

import java.util.ArrayList;

/**
 * 标题：顺时针打印矩阵
 * 题目描述
 * 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，例如，如果输入如下4 X 4
 * 矩阵： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
 * 则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.
 * 题目链接：
 * https://www.nowcoder.com/practice/9b4c81a02cd34f76be2659fa0d54342a?tpId=13&&tqId=11172&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz19 {

    public ArrayList<Integer> printMatrix2(int[][] matrix) {
        ArrayList<Integer> list = new ArrayList<>();
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return list;
        }
        int up = 0;
        int down = matrix.length - 1;
        int left = 0;
        int right = matrix[0].length - 1;
        while (true) {
            // 最上面一行
            for (int col = left; col <= right; col++) {
                list.add(matrix[up][col]);
            }
            // 向下逼近
            up++;
            // 判断是否越界
            if (up > down) {
                break;
            }
            // 最右边一行
            for (int row = up; row <= down; row++) {
                list.add(matrix[row][right]);
            }
            // 向左逼近
            right--;
            // 判断是否越界
            if (left > right) {
                break;
            }
            // 最下面一行
            for (int col = right; col >= left; col--) {
                list.add(matrix[down][col]);
            }
            // 向上逼近
            down--;
            // 判断是否越界
            if (up > down) {
                break;
            }
            // 最左边一行
            for (int row = down; row >= up; row--) {
                list.add(matrix[row][left]);
            }
            // 向右逼近
            left++;
            // 判断是否越界
            if (left > right) {
                break;
            }
        }
        return list;
    }


    public ArrayList<Integer> printMatrix(int[][] matrix) {
        ArrayList<Integer> result = new ArrayList<Integer>();
        int r1 = 0, r2 = matrix.length - 1, c1 = 0, c2 = matrix[0].length - 1;
        while (r1 <= r2 && c1 <= c2) {
            for (int i = c1; i <= c2; i++) {
                result.add(matrix[r1][i]);
            }
            for (int i = r1 + 1; i <= r2; i++) {
                result.add(matrix[i][c2]);
            }
            if (r1 != r2) {
                for (int i = c2 - 1; i >= c1; i--) {
                    result.add(matrix[r2][i]);
                }
            }
            if (c1 != c2) {
                for (int i = r2 - 1; i > r1; i--) {
                    result.add(matrix[i][c1]);
                }
            }
            r1++;
            r2--;
            c1++;
            c2--;
        }
        return result;
    }
}

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