重建二叉树

重建二叉树

题目

输入二叉树的先序遍历和中序遍历，重建一课二叉树

代码

#include<iostream>
#include<vector>
using namespace std;

/* 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) {
        TreeNode *root=new TreeNode(pre[0]);//必须使用new或malloc，否则局部变量会在下一循环被删除
        vector<int> vinLeft, vinRight;
        bool isLeft = true;
        //根据前序pre第一个元素将中序分成两部分
        for (int i = 0; i<vin.size(); i++){
            if (vin[i] == pre[0]){
                isLeft = false;
                continue;
            }
            if (isLeft) vinLeft.push_back(vin[i]);
            else vinRight.push_back(vin[i]);
        }
        vector<int> preLeft, preRight;
        //根据中序左右两部分大小将前序分成两部分
        for (int i = 1; i<pre.size(); i++){
            if (i <= vinLeft.size()) preLeft.push_back(pre[i]);
            else preRight.push_back(pre[i]);
        }
        //左子树迭代
        if (vinLeft.size() == 0) root->left = NULL;
        else root->left = reConstructBinaryTree(preLeft, vinLeft);
        //右子树迭代
        if (vinRight.size() == 0) root->right = NULL;
        else root->right = reConstructBinaryTree(preRight, vinRight);
        return root;
    }
};