题目: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。
代码(c/c++):
#include <iostream> #include <iterator> #include <vector> using namespace std; struct TreeNode { int val; TreeNode *left; TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; TreeNode* reConstructBinaryTree(vector<int> pre, vector<int> vin) { int pre_len = pre.size(); int in_len = vin.size(); if(pre_len == 0 || in_len == 0 || pre_len != in_len) return NULL; TreeNode *head = new TreeNode(pre[0]);//创建根节点 int root_ind = 0;//记录root在中序中的下标 for(int i = 0; i<pre_len; i++){ if(vin[i] == pre[0]){ root_ind = i; break; } } vector<int> in_left, in_right,pre_left, pre_right; for(int j = 0; j<root_ind; j++){ in_left.push_back(vin[j]); pre_left.push_back(pre[j+1]);//第一个为根根节点,跳过 } for(int j = root_ind+1; j<pre_len; j++){ in_right.push_back(vin[j]); pre_right.push_back(pre[j]); } //递归 head->right = reConstructBinaryTree(pre_right, in_right); head->left = reConstructBinaryTree(pre_left, in_left); return head; } //中序遍历,可以查看是否重建成功 void inorderTraverseRecursive(TreeNode *root) { if(root != NULL){ inorderTraverseRecursive(root->left); cout<<root->val<<" "; inorderTraverseRecursive(root->right); } } int main(){ int pre[] = {1,2,4,7,3,5,6,8}; int in[] = {4,7,2,1,5,3,8,6}; vector<int> pre_vec(pre, pre+8); vector<int> in_vec(std::begin(in), std::end(in)); // for(auto item: pre_vec) // cout<<item<<' '<<endl; // for(auto item: in_vec) // cout<<item<<' '<<endl; TreeNode *head ; head = reConstructBinaryTree(pre_vec, in_vec); inorderTraverseRecursive(head); return 0; }