顺时针打印矩阵（剑指offer_29）

题目描述

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下图的矩阵顺时针打印结果为：1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10。

 

解题思路

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
        ArrayList<Integer>  ret = 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++)
                ret.add(matrix[r1][i]);
            for(int i = r1+1; i <= r2; i++)   //注意边界条件1
                ret.add(matrix[i][c2]);
            if(r1 != r2) 
                for(int i = c2-1; i >= c1; i--) //注意边界条件2
                    ret.add(matrix[r2][i]);
            if(c1 != c2)
                for(int i = r2-1; i > r1; i--)  //注意边界条件3
                    ret.add(matrix[i][c1]);
            r1++;r2--;c1++;c2--;
        }
        return ret;
    }
}