由遍历序列构造二叉树

1. 根据前序中序确定二叉树
2. 根据后序中序确定二叉树
3. 根据层次中序确定二叉树
   注意，根据前序和后序无法确定一棵二叉树

#include <iostream>#include <stack>#include <queue>#include <string>#include <cstdlib>#include <fstream>using namespace std;#define ElemType chartypedef struct treeNode {    struct treeNode * lchild;    struct treeNode * rchild;    ElemType data;}treeNode,* tree;//递归前中后序void preOrder(tree & t) {    if (t) {        std::cout << t->data;        preOrder(t->lchild);        preOrder(t->rchild);    }}void inOrder(tree & t) {    if (t) {        inOrder(t->lchild);        std::cout << t->data;        inOrder(t->rchild);    }}void postOrder(tree & t) {    if (t) {        postOrder(t->lchild);        postOrder(t->rchild);        std::cout << t->data;    }}void levelOrder(tree & t) {    queue<tree> q;    if (t) {        q.push(t);        while (!q.empty()) {            tree temp = q.front();            cout << temp->data ;            q.pop();            if (temp->lchild)                q.push(temp->lchild);            if (temp->rchild)                q.push(temp->rchild);        }    }}//根据先序中序建立树void preInCreate(string pre_str, string in_str, tree & t) {    if (!pre_str.empty()&&!in_str.empty()) {      //数组内还有结点时，申请空间构造结点        t = (treeNode *)malloc(sizeof(treeNode));        t->data = pre_str[0];        int pos = in_str.find(pre_str[0]);        string lpstr = pre_str.substr(1, pos);        string rpstr = pre_str.substr(pos + 1, pre_str.length() - 1 - pos);        string listr = in_str.substr(0, pos);        string ristr = in_str.substr(pos + 1, in_str.length() - 1 - pos);        preInCreate(lpstr, listr, t->lchild);        preInCreate(rpstr, ristr, t->rchild);    }    else        t = NULL;}//根据后序中序建立树void postInCreate(string in_str, string post_str, tree & t) {    if (!in_str.empty() && !post_str.empty()) {        t = (treeNode*)malloc(sizeof(treeNode));        t->data = post_str[post_str.length() - 1];        int pos = in_str.find(post_str[post_str.length() - 1]);        string listr = in_str.substr(0, pos);        string ristr = in_str.substr(pos + 1, in_str.length() - 1 - pos);        string lpstr = post_str.substr(0, pos);        string rpstr = post_str.substr(pos, in_str.length() - 1 - pos);        postInCreate(listr, lpstr, t->lchild);        postInCreate(ristr, rpstr, t->rchild);    }    else        t = NULL;}int main() {    string pre_str;    string in_str;    string post_str;    tree t;    //std::cin >> pre_str >> in_str;    //preInCreate(pre_str, in_str, t);    postInCreate(in_str, post_str, t);    preOrder(t);    cout << endl;    //preInCreate(pre_str, in_str, t);    postInCreate(in_str, post_str, t);    inOrder(t);    cout << endl;    //preInCreate(pre_str, in_str, t);    postInCreate(in_str, post_str, t);    postOrder(t);    cout << endl;    //preInCreate(pre_str, in_str, t);    postInCreate(in_str, post_str, t);    levelOrder(t);    cout << endl;    system("PAUSE");    return EXIT_SUCCESS;}