Spiral Matrix

Given a matrix of m x n elements (m rows, n columns),
return all elements of the matrix in spiral order.

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Example
Given the following matrix:

[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5].

Tags Expand

Array Matrix

思路

• 来源
• 考察下标的运算,设置一个基本值,然后通过ij变化去求值

public class Solution {
    /**
     * @param matrix a matrix of m x n elements
     * @return an integer list
     */
    public List<Integer> spiralOrder(int[][] matrix) {
        // Write your code here
        if(matrix.length == 0) {
             return new ArrayList<Integer>();
        }

        List<Integer> result = new ArrayList<Integer>();
        // Initialize our four indexes
        int top = 0;
        int down = matrix.length - 1;
        int left = 0;
        int right = matrix[0].length - 1;

        while (true) {
            // Print top row
            for (int j = left; j <= right; ++j) {
                result.add(matrix[top][j]);
            }
            top++;
            if (top > down || left > right) break;

            //Print the rightmost column
            for (int i = top; i <= down; ++i) {
                result.add(matrix[i][right]);
            }
            right--;
            if (top > down || left > right) break;

            //Print the bottom row
            for (int j = right; j >= left; --j) {
                result.add(matrix[down][j]);
            }
            down--;
            if (top > down || left > right) break;

            //Print the leftmost column
            for (int i = down; i >= top; --i) {
                result.add(matrix[i][left]);
            }
            left++;
            if(top > down || left > right) break;
        }

        return result;
    }
}