【剑指offer】面试题 29. 顺时针打印矩阵

面试题 29. 顺时针打印矩阵

题目描述

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，例如，如果输入如下矩阵：

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.

解答过程

下图的矩阵顺时针打印结果为：1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10

Java 实现

import java.util.ArrayList;

public class Solution {

    public ArrayList<Integer> printMatrix(int [][] matrix) {

       ArrayList<Integer> res = new ArrayList<Integer>();

        if (matrix.length == 0) {

            return res;

        }

        int rowBegin = 0;

        int rowEnd = matrix.length-1;

        int colBegin = 0;

        int colEnd = matrix[0].length - 1;

        while (rowBegin <= rowEnd && colBegin <= colEnd) {

            // Traverse Right

            for (int j = colBegin; j <= colEnd; j ++) {

                res.add(matrix[rowBegin][j]);

            }

            rowBegin++;

            // Traverse Down

            for (int j = rowBegin; j <= rowEnd; j ++) {

                res.add(matrix[j][colEnd]);

            }

            colEnd--;

            if (rowBegin <= rowEnd) {

                // Traverse Left

                for (int j = colEnd; j >= colBegin; j --) {

                    res.add(matrix[rowEnd][j]);

                }

            }

            rowEnd--;

            if (colBegin <= colEnd) {

                // Traver Up

                for (int j = rowEnd; j >= rowBegin; j --) {

                    res.add(matrix[j][colBegin]);

                }

            }

            colBegin ++;

        }

        return res;

    }

}