<p>Given the <code>root</code> of a binary tree and an integer <code>targetSum</code>, return <em>all <strong>root-to-leaf</strong> paths where the sum of the node values in the path equals </em><code>targetSum</code><em>. Each path should be returned as a list of the node <strong>values</strong>, not node references</em>.</p>

<p>A <strong>root-to-leaf</strong> path is a path starting from the root and ending at any leaf node. A <strong>leaf</strong> is a node with no children.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/18/pathsumii1.jpg" style="width: 500px; height: 356px;" />
<pre>
<strong>Input:</strong> root = [5,4,8,11,null,13,4,7,2,null,null,5,1], targetSum = 22
<strong>Output:</strong> [[5,4,11,2],[5,8,4,5]]
<strong>Explanation:</strong> There are two paths whose sum equals targetSum:
5 + 4 + 11 + 2 = 22
5 + 8 + 4 + 5 = 22
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/18/pathsum2.jpg" style="width: 212px; height: 181px;" />
<pre>
<strong>Input:</strong> root = [1,2,3], targetSum = 5
<strong>Output:</strong> []
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> root = [1,2], targetSum = 0
<strong>Output:</strong> []
</pre>

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

<ul>
	<li>The number of nodes in the tree is in the range <code>[0, 5000]</code>.</li>
	<li><code>-1000 &lt;= Node.val &lt;= 1000</code></li>
	<li><code>-1000 &lt;= targetSum &lt;= 1000</code></li>
</ul>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> pathSum(TreeNode* root, int targetSum) {
        if (root == nullptr) {
            return {};
        }
        vector<vector<int>> paths;
        std::queue<std::pair<TreeNode*, int>> q;
        q.push({root, root->val});
        std::unordered_map<TreeNode*, TreeNode*> parent;
        parent[root] = nullptr;
        while (!q.empty()) {
            auto [node, value] = q.front();
            q.pop();
            if (value == targetSum && node->left == nullptr && node->right == nullptr) {
                paths.push_back({});  
                std::vector<int> &r = paths.back();
                TreeNode* p = node;
                while (p != nullptr) {
                    r.push_back(p->val);
                    p = parent[p];
                }
                std::reverse(r.begin(), r.end());
            }
            if (node->left != nullptr) {
                parent[node->left] = node;
                q.push({node->left, value + node->left->val});
            }
            if (node->right != nullptr) {
                parent[node->right] = node;
                q.push({node->right, value + node->right->val});
            }
        }
        return paths;
    }
};
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