算法--二叉树

1、根据前序遍历和中序遍历构造二叉树

#include <iostream>using namespace std;typedef struct BiNode {    char data;    struct BiNode *lchild;    struct BiNode *rchild;}BiNode, *BiTree;void CreateBiTree(BiTree &t, string presequence, string insequence) {    if(presequence.length()==0) {       t=NULL;        return;    }    char rootNode = presequence[0];//根    int index = insequence.find(rootNode);//根在中序序列中的位置    string lchild_insequence=insequence.substr(0, index);//左孩子的中序序列    string rchild_insequence=insequence.substr(index+1);//右孩子的中序序列    int lchild_length = lchild_insequence.length();    int rchild_length = rchild_insequence.length();    string lchild_presequence=presequence.substr(1, lchild_length);//左孩子的前序序列    string rchild_presequence=presequence.substr(1+lchild_length);//右孩子的前序序列    t = new BiNode;    if(t != NULL) {        t->data=rootNode;        CreateBiTree(t->lchild, lchild_presequence, lchild_insequence);        CreateBiTree(t->rchild, rchild_presequence, rchild_insequence);    }}void PreOrderTraverse(BiTree &t) {    if( t!= NULL ) {        cout << t->data;        PreOrderTraverse(t->lchild);        PreOrderTraverse(t->rchild);    }}void InOrderTraverse(BiTree &t) {    if( t!= NULL ) {        InOrderTraverse(t->lchild);        cout << t->data;        InOrderTraverse(t->rchild);    }}int main() {    BiTree t;    string presequence="ABCDEFG";    string insequence="CBEDAFG";    CreateBiTree(t, presequence, insequence);    PreOrderTraverse(t);    cout << endl;    InOrderTraverse(t);    return 0;}

---

#include <iostream>#include <vector>#include <algorithm>using namespace std;// Definition for binary treestruct TreeNode {    int val;    TreeNode *left;    TreeNode *right;    TreeNode(int x) : val(x), left(NULL), right(NULL) {}};class Solution {public:    TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {        if(pre.empty())            return NULL;        int root = pre.at(0);//根节点的值        TreeNode *t = new TreeNode(root);//根节点        int index = 0;//根节点在中序遍历中的位置        vector<int>::iterator iElement = find(vin.begin(), vin.end(), root);        if(iElement != vin.end()) {            index  = distance(pre.begin(), iElement);        }        vector<int> lVinSequence;//左中序序列        vector<int> rVinSequence;//右中序序列        lVinSequence.assign(vin.begin(),vin.begin()+index);        rVinSequence.assign(vin.begin()+index+1,vin.end());        int lLength = lVinSequence.size();//左先序序列长度        int rLength = rVinSequence.size();//右先序序列长度        vector<int> lPreSequence;//左先序序列        vector<int> rPreSequence;//右先序序列        lPreSequence.assign(pre.begin()+1,pre.begin()+lLength+1);        rPreSequence.assign(pre.begin()+lLength+2,pre.end());        t->left = reConstructBinaryTree(lPreSequence, lVinSequence);        t->right = reConstructBinaryTree(lPreSequence, rVinSequence);        return t;    }};void showVector(vector<int> v) {    for(vector<int>::iterator iter=v.begin(); iter != v.end(); ++iter) {        cout << *iter << " ";    }    cout << endl;}void showPreSequence(TreeNode *t) {    if( t!= NULL ) {        cout << t->val << " ";        showPreSequence(t->left);        showPreSequence(t->right);    }}void showInSequence(TreeNode *t) {    if( t!= NULL ) {        showPreSequence(t->left);        cout << t->val << " ";        showPreSequence(t->right);    }}int main() {    vector<int> pre;    vector<int> vin;    //前序遍历序列{1,2,4,7,3,5,6,8}    pre.push_back(1);pre.push_back(2);pre.push_back(4);pre.push_back(7);pre.push_back(3);pre.push_back(5);pre.push_back(6);pre.push_back(8);    //中序遍历序列{4,7,2,1,5,3,8,6}    vin.push_back(4);vin.push_back(7);vin.push_back(2);vin.push_back(1);vin.push_back(5);vin.push_back(3);vin.push_back(8);vin.push_back(6);    cout << "先序遍历: " ; showVector(pre);    cout << "中序遍历: " ; showVector(vin);//    vector<int>::iterator iElement = find(pre.begin(), pre.end(), 7);//    int nPosition;//    if(iElement != pre.end()) {//        nPosition = distance(pre.begin(), iElement);//        cout << "Value :" << *iElement << " ";//        cout << "find in the Vector at position :" << nPosition + 1 << endl;//    }//    vector<int> ltmp;//    vector<int> rtmp;//    ltmp.assign(pre.begin(), pre.begin()+nPosition);//    rtmp.assign(pre.begin()+nPosition+1, pre.end());//    showVector(ltmp);//    showVector(rtmp);////    ltmp.assign(pre.begin()+1, pre.begin()+4);//    rtmp.assign(pre.begin()+5, pre.end());//    showVector(ltmp);//    showVector(rtmp);    Solution s;    TreeNode *t  = s.reConstructBinaryTree(pre, vin);    showInSequence(t);    return 0;}