已知数的前序和中序遍历，求后序遍历和层序遍历的序列

树的存储结构定为链式存储结构，首先需要建树buildTree()，然后用递归遍历PostTraverse()产生后序遍历，借用队列实现层序遍历：

实现代码：

#include <iostream>
#include <string>
#include <queue>
using namespace std;

struct TreeNode{
    char val;
    TreeNode *left,*right;
};

TreeNode * bulidTree(string pre,string in){
    TreeNode * root =NULL;
    if (pre.length() > 0)
    {
        root = new TreeNode;
        root->val = pre[0];
        int index = in.find(pre[0]);

        root->left = bulidTree(pre.substr(1,index),in.substr(0,index));
        root->right = bulidTree(pre.substr(index+1),in.substr(index+1));
    }
    return root;
}

void PostTraverse(TreeNode * root){
    if (root != NULL)
    {
        PostTraverse(root->left);
        PostTraverse(root->right);
        cout<<root->val;
    }
}

void FTraverse(TreeNode * root)
{
    queue<TreeNode> Q;

    Q.push(*root);

    while(!Q.empty())
    {
        TreeNode tmp = Q.front();

        if(tmp.left!=NULL) Q.push(*tmp.left);

        if(tmp.right!=NULL) Q.push(*tmp.right);

        cout << tmp.val;

        Q.pop();
    }
}

    int main(){
    string prestr,instr;
    while(cin>>prestr>>instr){
        TreeNode * root =bulidTree(prestr,instr);
        PostTraverse(root);
        cout<<" ";
        FTraverse(root);
        cout<<endl;
    }
    return 0;
}