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<>();
        int r1 = 0;
        int r2 = matrix.length-1;
        int c1 = 0;
        int 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; i--)
                    list.add(matrix[i][c1]);
            r1++;
            r2--;
            c1++;
            c2--;
        }
        return list;
    }
}