题解 | #螺旋矩阵#

import java.util.*;


public class Solution {
    public ArrayList<Integer> spiralOrder (int[][] matrix) {
        // write code here
        ArrayList<Integer> res = new ArrayList<>();
        if(matrix.length == 0)
            return res;
        // 定义四个指针，并且充当边界限制的作用
        int top = 0, bottom = matrix.length-1;
        int left = 0, right = matrix[0].length-1;
       
        while(true){
            //上面  左到右
            for(int i = left; i <= right; i++){
                res.add(matrix[top][i]);
            } ++top;
            if(top > bottom) break;
 
            //右边 上到下
            for(int i = top; i <= bottom; i++){
                res.add(matrix[i][right]);
            }--right;
            if(right < left) break;
 
            //下面  右到左
            for(int i = right; i>=left; i--){
                res.add(matrix[bottom][i]);
            }--bottom;
            if(bottom < top) break;
 
            //左边 下到上
            for(int i = bottom; i>=top; i--){
                res.add(matrix[i][left]);
            }left++;
            if(left > right) break;           
        }
        return res;
    }
}