LeetCode54 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]. （Medium）

分析：

题目没有什么复杂的算法要应用，就是一行一列输出，处理好细节即可。

比较清晰的写法是搞一个rowBegin, rowEnd, colBegin, colEnd， 并在处理完一行/一列后更新值，并判断是否仍然满足 rowBegin <= rowEnd && colBegin <= colEnd

代码：

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        vector<int> result;
        if (matrix.size() == 0) {
            return result;    
        }
        int m = matrix.size(), n = matrix[0].size();
        int rowBegin = 0, rowEnd = m - 1, colBegin = 0, colEnd = n - 1;
        while (rowBegin <= rowEnd && colBegin <= colEnd) {
            for (int i = colBegin; i <= colEnd; ++i ) {
                result.push_back(matrix[rowBegin][i]);
            }
            rowBegin++;
            if (rowBegin > rowEnd) {
                break;
            }
            for (int i = rowBegin; i <= rowEnd; ++i) {
                result.push_back(matrix[i][colEnd]);
            }
            colEnd--;
            if (colBegin > colEnd) {
                break;
            }
            for (int i = colEnd; i >= colBegin; --i) {
                result.push_back(matrix[rowEnd][i]);
            }
            rowEnd--;
            if (rowBegin > rowEnd) {
                break;
            }
            for (int i = rowEnd; i>= rowBegin; --i) {
                result.push_back(matrix[i][colBegin]);
            }
            colBegin++;
        }
        return result;
    }
};