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  • 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[0];
      }
      void helper(TreeNode* root, vector<string>& a, string parent){
        if(!root) return;
        string tmpc(1,(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);
      }
    };
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  • 原文地址:https://www.cnblogs.com/ethanhong/p/10350217.html
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