【剑指Offer】29. 顺时针打印矩阵

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
        ArrayList<Integer> rel = new ArrayList<>();
        int r1 = 0, r2 = matrix.length - 1, c1 = 0, c2 = matrix[0].length - 1;
        
        while(r1 <= r2 && c1 <= c2) {
            for(int i = c1; i <= c2; i++)
                rel.add(matrix[r1][i]);
            for(int i = r1+1; i <= r2; i++)
                rel.add(matrix[i][c2]);
            if(r1 != r2)
                for(int i = c2-1; i >= c1; i--)
                    rel.add(matrix[r2][i]);
            if(c1 != c2)
                for(int i = r2-1; i > r1; i--)
                    rel.add(matrix[i][c1]);
            
            r1++; r2--; c1++; c2--;
        }
        
        return rel;
    }
}