树

一，Construct Binary Tree from Preorder and Inorder Traversal

题目描述

Given preorder and inorder traversal of a tree, construct the binary tree.

我的代码

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    TreeNode* buildTree(vector<int> &preorder, vector<int> &inorder) {        return Helper(preorder, 0, preorder.size()-1, inorder, 0, inorder.size()-1);    }    TreeNode* Helper(vector<int> &preorder, int begin1, int end1, vector<int> &inorder, int begin2, int end2){        if(begin1 > end1){            return NULL;        } else if(begin1 == end1){            return new TreeNode(preorder[begin1]);        } else {            TreeNode* root = new TreeNode(preorder[begin1]);            int i = begin2;            for(; i <= end2; i ++){                if(inorder[i] == preorder[begin1]){                    break;                }            }            int leftlen = i - begin2;            root->left = Helper(preorder, begin1 + 1, begin1 + leftlen, inorder, begin2, begin2 + leftlen - 1);            root->right = Helper(preorder, begin1 + leftlen + 1, end1, inorder, begin2 + leftlen + 1, end2);            return root;        }    }};