剑指Offer_编程题_4

Posted 2020-11-01 gaoren

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。

/**
 * 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 vinSize = vin.size();
        if(vinSize == 0) return NULL;
        vector<int>pre_left,pre_right,vin_left,vin_right;
        int val = pre[0];
        int i;
        for(i = 0; i < vinSize; i ++) {
            if(vin[i] == val){
                break;
            }
        }
        int index = i;
        TreeNode* tree = new TreeNode(val);
        for(i = 0; i < vinSize; i++ ) {
            if(i < index) {
                vin_left.push_back(vin[i]);
                pre_left.push_back(pre[i+1]);
            } else if(i > index) {
                vin_right.push_back(vin[i]);
                pre_right.push_back(pre[i]);
            }
        }
        tree->left = reConstructBinaryTree(pre_left,vin_left);
        tree->right = reConstructBinaryTree(pre_right,vin_right);
        return tree;
    }
    
};