package web; /**

* @program LeetNiu

* @description: 顺时针打印矩阵

* @author: mf

* @create: 2020/01/10 16:22

*/

import java.util.ArrayList;

/**

* 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.

*/

public class T19 {

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

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

if (matrix == null || matrix.length == 0 || matrix[0].length == 0) return list;

int start = 0;

int rows = matrix.length;

int cols = matrix[0].length;

while (rows > start * 2 && cols > start * 2) {

print(matrix, rows, cols, start, list);

start++;

}

return list;

}

/**

* 打印圈

* @param arr

* @param rows

* @param cols

* @param start

* @param list

*/

private void print(int[][] arr, int rows, int cols, int start, ArrayList<Integer> list) {

int endX = cols - 1 - start;

int endY = rows - 1 - start;

// 从左到右打印一行

for(int i = start; i <= endX; i++) {

list.add(arr[start][i]);

}

// 从上到下打印一列

if(start < endY) {

for(int i = start + 1; i <= endY; i++){

list.add(arr[i][endX]);

}

}

// 从右往左打印哟行

if(start < endX && start < endY) {

for(int i = endX - 1; i >= start; i--) {

list.add(arr[endY][i]);

}

}

// 从下往上打印一列

if(start < endX && start < endY) {

for(int i = endY - 1; i >= start + 1; i--) {

list.add(arr[i][start]);

}

}

}

}