leetcode

0988.cpp (707B)

 class Solution {
   public:
     string smallestFromLeaf(const TreeNode *root) const {
         queue<pair<const TreeNode *, string>> q;
         q.emplace(root, "");
 
         string res(16, 'z');
         while (!q.empty()) {
             for (int k = q.size(); k > 0; k--) {
                 auto [root, s] = q.front();
                 q.pop();
                 s += 'a' + root->val;
 
                 if (root->left) q.emplace(root->left, s);
                 if (root->right) q.emplace(root->right, s);
 
                 if (!root->left && !root->right) {
                     reverse(begin(s), end(s));
                     res = min(res, s);
                 }
             }
         }
 
         return res;
     }
 };