498 Diagonal Traverse 对角线遍历

详见：https://leetcode.com/problems/diagonal-traverse/description/

C++：

class Solution {
public:
    vector<int> findDiagonalOrder(vector<vector<int>>& matrix)
    {
        if (matrix.empty() || matrix[0].empty())
        {
            return {};
        }
        int m = matrix.size(), n = matrix[0].size(), r = 0, c = 0, k = 0;
        vector<int> res(m * n);
        vector<vector<int>> dirs{{-1,1}, {1,-1}};
        for (int i = 0; i < m * n; ++i)
        {
            res[i] = matrix[r][c];
            r += dirs[k][0];
            c += dirs[k][1];
            if (r >= m)
            {
                r = m - 1;
                c += 2;
                k = 1 - k;
            }
            if (c >= n)
            {
                c = n - 1;
                r += 2;
                k = 1 - k;
            }
            if (r < 0)
            {
                r = 0;
                k = 1 - k;
            }
            if (c < 0)
            {
                c = 0;
                k = 1 - k;
            }
        }
        return res;
    }
};

参考：http://www.cnblogs.com/grandyang/p/6414461.html