Java 算法题 由简入深 牛客版

描述:

给定一个m x n大小的矩阵(m行,n列),按螺旋的顺序返回矩阵中的所有元素

数据范围:

0≤n,m≤10，矩阵中任意元素都满足 |val| ≤100

要求：空间复杂度 O(nm)O(nm) ，时间复杂度 O(nm)O(nm)

实例:

输入:[[1,2,3],[4,5,6],[7,8,9]]

返回:[1,2,3,6,9,8,7,4,5]

输入:[]

返回:[]

import java.util.ArrayList;
public class Solution {
    public ArrayList spiralOrder(int[][] matrix) {
         ArrayList res = new ArrayList<>();
        if(matrix.length == 0) return res;
        int count = 0, row = matrix.length, column = matrix[0].length;
        int total = row * column;
        int up = 0, down = row - 1, left = 0, right = column - 1;
        while(count < total){
            for(int i = left; i <= right && count < total; i++){
                res.add(matrix[up][i]);
                count++;
            }
            up++;
            for(int i = up; i <= down && count < total; i++){
                res.add(matrix[i][right]);
                count++;
            }
            right--;
            for(int i = right; i >= left && count < total; i--){
                res.add(matrix[down][i]);
                count++;
            }
            down--;
            for(int i = down; i >= up && count < total; i--){
                res.add(matrix[i][left]);
                count++;
            }
            left++;
        }
        return res;
    }
}