1. 054

spiral-matrix

2. 算法

http://www.acmerblog.com/leetcode-solution-spiral-matrix-6261.html

• 复杂度：O(nm)

3. 代码

class Solution {
//key observe: when any component is done, its beginX,endX or beginY,endX will change  
public:
    vector<int> spiralOrder(vector<vector<int> >& matrix) {
        vector<int> result;
        if (matrix.empty()) return result;
        int beginX = 0, endX = matrix[0].size() - 1;
        int beginY = 0, endY = matrix.size() - 1;
        while (true) {
            // From left to right  
            for (int i = beginX; i <= endX; ++i)
                result.push_back(matrix[beginY][i]);
            if (++beginY > endY) break;
            // From top down  
            for (int i = beginY; i <= endY; ++i)
                result.push_back(matrix[i][endX]);
            if (beginX > --endX) break;
            // From right to left  
            for (int i = endX; i >= beginX; --i)
                result.push_back(matrix[endY][i]);
            if (beginY > --endY) break;
            // From bottom up  
            for (int i = endY; i >= beginY; --i)
                result.push_back(matrix[i][beginX]);
            if (++beginX > endX) break;
        }
        return result;
    }
};