先序，中序建立二叉树

由二叉树的先序和中序序列建立二叉树
非常经典的算法，先序序列确定根，中序序列确定左右子树，递归即可。

TreeNode* Tree:: BuildTree(string &Pre, string &In,string d){
    //cout <<d<< "=======================================" << endl;
    //cout <<d<< "Pre=" << Pre << ",In=" << In << endl;
    if (Pre.size() == 0 || In.size() == 0){
        return nullptr;
    }else{
        TreeNode *cur=new TreeNode(Pre[0]);
        cout <<d<< "create node " << Pre[0] << endl;
        int rooti = In.find(Pre[0]);
        d += "    ";
        cur->left=BuildTree(Pre.substr(1,rooti ), In.substr(0, rooti),d);
        cur->right=BuildTree(Pre.substr(rooti + 1, Pre.size()), In.substr(rooti + 1, In.size()),d);
        return cur;
    }
}

---

BuildTree(string(“ABDEHJKLMNCFGI”),string(“DBJHLKMNEAFCGI”),” “);
上面序列建成的树形状如图：

二叉树打印见：
http://blog.youkuaiyun.com/u010909667/article/details/54972495