LC 988. Smallest String Starting From Leaf

Given the root of a binary tree, each node has a value from 0 to 25 representing the letters 'a' to 'z': a value of 0 represents 'a', a value of 1represents 'b', and so on.

Find the lexicographically smallest string that starts at a leaf of this tree and ends at the root.

(As a reminder, any shorter prefix of a string is lexicographically smaller: for example, "ab" is lexicographically smaller than "aba". A leaf of a node is a node that has no children.)

Runtime: 4 ms, faster than 100.00% of C++ online submissions for Smallest String Starting From Leaf.

Memory Usage: 884.7 KB, less than 100.00% of C++ online submissions for Smallest String Starting From Leaf.

class Solution {

public:

  string smallestFromLeaf(TreeNode* root) {

    vector<string> a;

    helper(root, a, "");

    sort(a.begin(), a.end());

    return a[];

  }

  void helper(TreeNode* root, vector<string>& a, string parent){

    if(!root) return;

    string tmpc(,(char)('a'+root->val));

    string tmps = tmpc + parent;

    if(!root->left && !root->right){

      a.push_back(tmps);

      return;

    }

    helper(root->left, a, tmps);

    helper(root->right, a, tmps);

  }

};

巴特西

LC 988. Smallest String Starting From Leaf

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