LeetCode 129. Sum Root to Leaf Numbers

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    
    static constexpr const size_t npos = static_cast<size_t>(-1);
    
    struct WayPoint{
        size_t last;
        TreeNode *node;
    };
    
    unordered_map<size_t, WayPoint> wayPoints;
    
    size_t AllocateWayPoint(){
        size_t next = wayPoints.size();
        wayPoints.insert(move(make_pair(next, WayPoint{})));
        return next;
    }
    
    int sumNumbers(TreeNode* root) {
        wayPoints.clear();
        
        if(root == nullptr){
            return 0;
        }
        
        vector<size_t> endPoints;
        
        auto head = AllocateWayPoint();
        wayPoints[head].last = npos;
        wayPoints[head].node = root;
        
        queue<size_t> myQueue; 
        myQueue.push(head);
        
        while(!myQueue.empty()){
            auto frontId = myQueue.front();
            myQueue.pop();
            
            const auto &front = wayPoints[frontId];
            
            bool isLeaf = true;
            if(front.node->left != nullptr){
                isLeaf = false;
                auto leftId = AllocateWayPoint();
                wayPoints[leftId].last = frontId;
                wayPoints[leftId].node = front.node->left;
                myQueue.push(leftId);
            }
            if(front.node->right != nullptr){
                isLeaf = false;
                auto rightId = AllocateWayPoint();
                wayPoints[rightId].last = frontId;
                wayPoints[rightId].node = front.node->right;
                myQueue.push(rightId);
            }
            
            if(isLeaf){
                endPoints.push_back(frontId);
            }
            
        }
        
        int allSum = 0;
        for(auto point : endPoints){
            int times = 1;
            while(point != npos){
                allSum += wayPoints[point].node->val * times;
                times *= 10;
                point = wayPoints[point].last;
            }
        }
        
        return allSum;
    }
};