面试题07

输入某二叉树的前序遍历和中序遍历的结果，请重建该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。

例如，给出

前序遍历 preorder = [3,9,20,15,7]
中序遍历 inorder = [9,3,15,20,7]

返回如下的二叉树：

    3
   / \
  9  20
    /  \
   15   7

限制：

• 0 <= 节点个数 <= 5000

注意：本题与主站 105 题重复：https://leetcode-cn.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/

Solutions

• check problem 105 for more solutions.

• recursion

/**
 * 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:
    TreeNode * buildTree(vector<int> & preorder, vector<int> & inorder, int & cur, int lo, int hi) {
        if (hi < lo)
            return nullptr;
        TreeNode * root = new TreeNode(preorder[++cur]);
        int mid = lo;
        while (inorder[mid] != preorder[cur])
            mid++;
        root->left = buildTree(preorder, inorder, cur, lo, mid - 1);
        root->right = buildTree(preorder, inorder, cur, mid + 1, hi);

        return root;
    }

    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        int cur = -1;
        return buildTree(preorder, inorder, cur, 0, inorder.size() - 1);
    }
};