<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 {
    struct SparseMatrixCellInfo {
        size_t x;
        size_t y;
        size_t rowColSum;
        int value;
    };

public:
    std::vector<int> findDiagonalOrder(std::vector<std::vector<int>>& nums) {
        std::vector<SparseMatrixCellInfo> processedNums{};

        for (size_t i = 0; i < nums.size(); ++i) {
            for (size_t j = 0; j < nums[i].size(); ++j) {
                processedNums.push_back({i, j, i + j, nums[i][j]});
            }
        }

        std::sort(processedNums.begin(), processedNums.end(), [](const auto& left, const auto& right) {
            if (left.rowColSum != right.rowColSum) {
                return left.rowColSum < right.rowColSum;
            }

            // We want to go from the furthest left element of the diagonal onwards
            return left.y < right.y;
        });

        std::vector<int> result{};
        for (const auto& cellInfo : processedNums) {
            result.push_back(cellInfo.value);
        }
        return result;
    }
};
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