根据树的先序和中序来创建一棵树

只知道先序序列和后序序列是无法求出唯一的树，所以不做讨论。

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;

struct BinaryTreeNode
{
    char c;
    BinaryTreeNode *lchild, *rchild;
    BinaryTreeNode()
    {
        lchild = NULL, rchild = NULL;
    }
};
struct BinaryTreeNode *root1,*root2;

char preorder[100], inorder[100], postorder[100];

void preSearch(BinaryTreeNode *root)   //先序遍历树
{
    if(root != NULL)
    {
        printf("%c", root->c);
        preSearch(root->lchild);
        preSearch(root->rchild);
    }
    return ;
}

void midSearch(BinaryTreeNode *root)   //中序遍历树
{
    if(root != NULL)
    {
        midSearch(root->lchild);
        printf("%c", root->c);
        midSearch(root->rchild);
    }
    return ;
}

void postSearch(BinaryTreeNode *root)  //后序遍历树
{
    if(root != NULL)
    {
        postSearch(root->lchild);
        postSearch(root->rchild);
        printf("%c", root->c);
    }
    return ;
}

void BuildTreeFromPreAndMid(BinaryTreeNode * &root, int ll, int lr, int len, int &now)//根据中序和先序求树
{
    root = new BinaryTreeNode();
    root->c = *(preorder + now);
    int pos = (int)(strchr(inorder, *(preorder + now)) - inorder); //查找字符串中首次出现某个字符的位置
    now++;
    if(now >= len)
        return ;
    if(pos - 1 >= ll)
    {
        BinaryTreeNode *t = new BinaryTreeNode();
        root->lchild = t;
        BuildTreeFromPreAndMid(root->lchild, ll, pos - 1, len, now);
    }
    if(pos + 1 <= lr)
    {
        BinaryTreeNode *t = new BinaryTreeNode();
        root->rchild = t;
        BuildTreeFromPreAndMid(root->rchild, pos + 1, lr, len, now);
    }
}

void BuildTreeFromPostAndMid(BinaryTreeNode * &root, int ll, int lr, int len, int &now)//根据中序和后序求树
{
    root = new BinaryTreeNode();
    root->c = *(postorder + now);
    int pos = (int)(strchr(inorder, *(postorder + now)) - inorder);
    now--;
    if(now < 0)
        return ;
    if(pos + 1 <= lr)
    {
        BinaryTreeNode *t = new BinaryTreeNode();
        root->rchild = t;
        BuildTreeFromPostAndMid(root->rchild, pos + 1, lr, len, now);
    }
    if(pos - 1 >= ll)
    {
        BinaryTreeNode *t = new BinaryTreeNode();
        root->lchild = t;
        BuildTreeFromPostAndMid(root->lchild, ll, pos - 1, len, now);
    }
}

//释放二叉树
inline void DeleteBinaryTree(BinaryTreeNode * &root)
{
    if(root)
    {
        DeleteBinaryTree(root->lchild);    //释放左子树
        DeleteBinaryTree(root->rchild);    //释放右子树
        delete root;          //释放根结点
    }
}

int main(void)
{
    gets(preorder);
    gets(inorder);
    //gets(postorder);
    int now = 0;
    BuildTreeFromPreAndMid(root1, 0, strlen(preorder) - 1, strlen(preorder), now);

    //int now2 = strlen(postorder)-1;
    //BuildTreeFromPostAndMid(root2, 0, strlen(postorder) - 1, strlen(postorder), now2);

    postSearch(root1);
    puts("");
    DeleteBinaryTree(root1);
    /*preSearch(root2);
    puts("");
    DeleteBinaryTree(root2);*/
    return 0;
}