题目描述

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。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。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

先求出根节点，可以轻易判断左右子树所属的数组部分，将其分割，通过递归法重建二叉树。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* reConstructBinaryTree(vector<int> pre, vector<int> vin) {
        if (pre.empty() || vin.empty() || pre.size() != vin.size()) {
            return NULL;
        }
        int i;
        vector<int> pre_left, pre_right, vin_left, vin_right;
        for (i = 0; i < pre.size(); i++) {
            if (pre[0] == vin[i])
                break;
            else {
                pre_left.push_back(pre[i + 1]);
                vin_left.push_back(vin[i]);
            }
        }
        for (int j = i + 1; j < pre.size(); j++) {
            pre_right.push_back(pre[j]);
            vin_right.push_back(vin[j]);
        }
        TreeNode* binaryTree = new TreeNode(pre[0]);
        binaryTree->left = reConstructBinaryTree(pre_left, vin_left);
        binaryTree->right = reConstructBinaryTree(pre_right, vin_right);
        return binaryTree;
    }
};