4 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) {
        int len = pre.size();
        if(len == 0) return NULL;
        int idx;
        for(int i = 0; i < len; ++i){
            if(vin[i] == pre[0]){
                idx = i;
                break;
            }
        }

        vector<int> pre_left, pre_right, vin_left, vin_right;

        for(int i = 0; i< idx; ++i){
            pre_left.push_back(pre[i+1]);
            vin_left.push_back(vin[i]);
        }

        for(int i = idx + 1; i < len; ++i){
            pre_right.push_back(pre[i]);
            vin_right.push_back(vin[i]);
        }

        TreeNode* head = new TreeNode(pre[0]);
        head->left = reConstructBinaryTree(pre_left, vin_left);
        head->right = reConstructBinaryTree(pre_right, vin_right);
        return head;

    }
};