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# 題目敘述

Given an m x n matrix , return all elements of the matrix in spiral order.

# Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [1,2,3,6,9,8,7,4,5]

# Example 2:

Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

# 解題思路

# Solution

import java.util.ArrayList;
import java.util.List;
class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        int rows = matrix.length;
        int cols = matrix[0].length;
        List<Integer> ans = new ArrayList<>();
        if (rows == 0) {
            return ans;
        }
        
        int left = 0, right = cols - 1, top = 0, bottom = rows - 1;
        while (left <= right && top <= bottom) {
            for (int i = left; i <= right; i++) {
                ans.add(matrix[top][i]);
            }
            top++;
            
            for (int i = top; i <= bottom; i++) {
                ans.add(matrix[i][right]);
            }
            right--;
            
            if (top <= bottom) {
                for (int i = right; i >= left; i--) {
                    ans.add(matrix[bottom][i]);
                }
                bottom--;
            }
            
            if (left <= right) {
                for (int i = bottom; i >= top; i--) {
                    ans.add(matrix[i][left]);
                }
                left++;
            }
        }
        
        return ans;
    }
}




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