Leetcode: Spiral Matrix

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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].

不难，需要注意边界case。

class Solution {public:    vector<int> spiralOrder(vector<vector<int> > &matrix) {        vector<int> result;        int rows = matrix.size();        if (rows == 0) return result;        int cols = matrix[0].size();        if (cols == 0) return result;                int level = min(rows, cols);        int i = 0;        for (; i < level / 2; ++i) {            for (int j = i; j < cols - i - 1; ++j) {                result.push_back(matrix[i][j]);            }            for (int j = i; j < rows - i - 1; ++j) {                result.push_back(matrix[j][cols-i-1]);            }            for (int j = cols - i - 1; j > i; --j) {                result.push_back(matrix[rows-i-1][j]);            }            for (int j = rows - i - 1; j > i; --j) {                result.push_back(matrix[j][i]);            }        }                if (level % 2 != 0) {            if (rows <= cols) {                for (int j = i; j < cols - i; ++j) {                    result.push_back(matrix[i][j]);                }            }            else {                for (int j = i; j < rows - i; ++j) {                    result.push_back(matrix[j][i]);                }            }        }                return result;    }};

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