剑指offer:面试题20、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.

代码示例

import java.util.ArrayList;
import java.util.List;

public class Offer20 {
    public static void main(String[] args) {
        int[][] matrix = {
                {1, 2, 3, 4},
                {5, 6, 7, 8},
                {9, 10,11,12},
                {13,14,15,16}
        };
        Offer20 testObj = new Offer20();
        List<Integer> res = testObj.printMatrix(matrix);
        System.out.println(res);
    }

    public List<Integer> printMatrix(int[][] matrix) {
        List<Integer> res = new ArrayList<>();
        int rowLeft = 0;
        int rowRight = matrix.length - 1;
        int colLeft = 0;
        int colRight = matrix[0].length - 1;
        while (rowLeft <= rowRight && colLeft <= colRight) {
            //先向右
            for (int i = rowLeft; i <= rowRight; i++) {
                res.add(matrix[rowLeft][i]);
            }
            //向下
            for (int i = rowLeft + 1; i <= rowRight; i++) {
                res.add(matrix[i][rowRight]);
            }
            //防止打印同一行
            if (rowLeft != rowRight) {
                //向左
                for (int i = rowRight - 1; i >= rowLeft; i--) {
                    res.add(matrix[rowRight][i]);
                }
            }
            if (colLeft != colRight) {
                //向上
                for (int i = rowRight - 1; i > rowLeft; i--) {
                    res.add(matrix[i][colLeft]);
                }
            }
            rowLeft++;
            rowRight--;
            colLeft++;
            colRight--;
        }
        return res;
    }
}