【LeetCode】从前序与中序遍历序列构造二叉树

链接: 从前序与中序遍历序列构造二叉树

题目描述

算法分析

编程代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:

    TreeNode* _bulid(vector<int>& preorder,vector<int>& inorder,int inbegin,int& orderi,int inend)
    {
        if(inbegin > inend)
        {
            return nullptr;
        }
        
        TreeNode* root = new TreeNode(preorder[orderi]);

        //找到中序遍历的根节点
        int rooti = inbegin;
        while(rooti <= inend)
        {
            if(preorder[orderi] == inorder[rooti])
            {
                orderi++;
                break;
            }
            rooti++;
        }
        root->left = _bulid(preorder,inorder,inbegin,orderi,rooti-1);
        root->right = _bulid(preorder,inorder,rooti+1,orderi,inend);
        return root;
    }

    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        
        int i = 0;
        TreeNode* root =_bulid(preorder,inorder,0,i,inorder.size()-1);
        return root;
    }
};