题目

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思路

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Code

/**
 * 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) {
        int prelen = pre.size();

        if(prelen == 0)    //递归终止条件： 前序数组，中序数组为0, 返回值为NULL
            return NULL;
        vector<int> preleft, preright, vinleft, vinright;    //子前序序列，子中序序列
        int gen;
        TreeNode *root = new TreeNode(pre[0]);               
        //寻找根在中序序列数组中的位置
        for(int i = 0; i < prelen; i++)
        {
            if(vin[i] == pre[0])
            {
                gen = i;
                break;
            }
        }
        //填充左子前序序列 [1, gen]，左子中序序列
        for(int i = 1; i <= gen; i++)
        {
            preleft.push_back(pre[i]);
            vinleft.push_back(vin[i-1]);
        }
        //填充右子前序序列 [gen+1, prenlen) ， 右子中序序列
        for(int i = gen+1; i < prelen; i++)
        {
            preright.push_back(pre[i]);
            vinright.push_back(vin[i]);
        }
        //递归左右子树
        root->left = reConstructBinaryTree(preleft, vinleft);
        root->right = reConstructBinaryTree(preright, vinright);

        return root;        
    }
};