<p>Given a 2D integer array <code>nums</code>, return <em>all elements of </em><code>nums</code><em> in diagonal order as shown in the below images</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/04/08/sample_1_1784.png" style="width: 158px; height: 143px;" />
<pre>
<strong>Input:</strong> nums = [[1,2,3],[4,5,6],[7,8,9]]
<strong>Output:</strong> [1,4,2,7,5,3,8,6,9]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/04/08/sample_2_1784.png" style="width: 230px; height: 177px;" />
<pre>
<strong>Input:</strong> nums = [[1,2,3,4,5],[6,7],[8],[9,10,11],[12,13,14,15,16]]
<strong>Output:</strong> [1,6,2,8,7,3,9,4,12,10,5,13,11,14,15,16]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i].length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= sum(nums[i].length) &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i][j] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:

    struct comparisonF {
        constexpr bool operator() (pair<int, int>& a, pair<int, int>& b) const noexcept {
            if ( (a.first + a.second) != (b.first + b.second) ) {
                return (a.first + a.second) > (b.first + b.second);
            }

            return a.second > b.second;
        }
    };

    vector<int> findDiagonalOrder(vector<vector<int>>& nums) {
        std::priority_queue< std::pair<int, int> , std::vector< std::pair< int, int> >, comparisonF> pq_;
        //std::priority_queue<std::pair<int, int>> pq_;

        for (int i=0; i<nums.size(); i++)
        {
            for (int q=0; q<nums[i].size(); q++)
            {
                pq_.push(std::make_pair(i, q));
            }
        }


        vector<int> res;
        while (!pq_.empty())
        {
            std::pair<int, int> top = pq_.top();
            pq_.pop();

            res.push_back(nums[top.first][top.second]);
        }

        return res;
    }
};
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