题解 | #顺时针打印矩阵#

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
        ArrayList<Integer> list = new ArrayList<>();

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

        int r1 = 0, r2 = matrix.length - 1;
        int c1 = 0, c2 = matrix[0].length - 1;

        while(r1 <= r2 && c1 <= c2){
            for(int i = c1; i <= c2; ++i){
                list.add(matrix[r1][i]);
            }

            for(int i = r1 + 1; i <= r2; ++i){
                list.add(matrix[i][c2]);
            }

            if(r1 != r2){
                for(int i = c2 - 1; i >= c1; --i){
                    list.add(matrix[r2][i]);
                }
            }

            if(c1 != c2){
                for(int i = r2 - 1; i >= r1 + 1; --i){
                    list.add(matrix[i][c1]);
                }
            }
            r1++;
            r2--;
            c1++;
            c2--;
        }

        return list;
    }
}