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.

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int[][] matrix) {
		int left = 0, right = matrix[0].length - 1, top = 0, boom = matrix.length - 1;// 记录四个角的位置
		ArrayList<Integer> list = new ArrayList<Integer>();

		while ((right > left) && (boom > top)) {
			for (int i = left; i <= right; i++) {// 从左到右
				list.add(matrix[top][i]);
			}
			for (int i = top + 1; i <= boom; i++) {// 上到下
				list.add(matrix[i][right]);
			}
			for (int i = right - 1; i >= left; i--) {// 右到左
				list.add(matrix[boom][i]);
			}
			for (int i = boom - 1; i > top; i--) {// 下到上
				list.add(matrix[i][left]);
			}
			left++;
			right--;
			top++;
			boom--;
		}

		if ((boom == top) && (left < right)) {// 单独剩下一行的情况
			for (int i = left; i <= right; i++) {
				list.add(matrix[top][i]);
			}
		}
		if ((left == right) && (boom > top)) {// 单独剩下一列的情况
			for (int i = top; i <= boom; i++) {
				list.add(matrix[i][left]);
			}
		}
		if ((boom == top) && (right == left)) {// 单独剩下一个元素的情况
			list.add(matrix[left][boom]);
		}
		return list;
	}
}