54. Spiral Matrix

题目：

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

For 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].

链接：https://leetcode.com/problems/spiral-matrix/#/description

4/19/2017

3ms, 27%

自己不会，抄别人的

思路是保存4个边界，每次循环完更新边界值，并且检查总的输出量。

第8行的判断可以用过left <= right, top <= bottom来检查

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> ret = new ArrayList<Integer>();
        if (matrix.length == 0 || matrix[0].length == 0) return ret;
        int count = matrix.length * matrix[0].length;
        int left = 0, right = matrix[0].length - 1, top = 0, bottom = matrix.length - 1;

        while (count > 0) {
            for (int i = left; i <= right; i++) {
                ret.add(matrix[top][i]);
                count--;
            }
            top++;
            if (count > 0) {
                for (int i = top; i <= bottom; i++) {
                    ret.add(matrix[i][right]);
                    count--;
                }
                right--;
            }
            if (count > 0) {
                for (int i = right; i >= left; i--) {
                    ret.add(matrix[bottom][i]);
                    count--;
                }
                bottom--;
            }
            if (count > 0) {
                for (int i = bottom; i >= top; i--) {
                    ret.add(matrix[i][left]);
                    count--;
                }
                top++;
            }
        }
        return ret;
    }
}

https://discuss.leetcode.com/topic/3713/super-simple-and-easy-to-understand-solution

更多讨论：

https://discuss.leetcode.com/category/62/spiral-matrix