剑指Offer-- 重建二叉树  前序中序建立二叉树

AC代码：

package algorithm;import common.TreeNode;/** * 类说明 *  * <pre> * Modify Information: * Author        Date          Description * ============ =========== ============================ * DELL          2017年5月17日    Create this file * </pre> *  */public class ReConstructBinaryTree {        public static TreeNode reConstructBinaryTree(int [] pre,int [] in) {             /**       * 在C/C++中可以用指针直接标识开始 和结束 *a a++ 就可以标识数组情况 但是对Java ,可以使用数组下标的方式标识起点个结束点       */      TreeNode root = constructBiTree(pre, 0, pre.length-1, in, 0, in.length-1);              return root;            }        public static TreeNode constructBiTree(int[] pre ,int startPre, int endPre, int[] in ,int startIn, int endIn){       //       System.out.println("startPre:"+startPre);       if(startPre >endPre || startIn > endIn){           return null;       }       TreeNode root = new TreeNode(pre[startPre]);       // i 指的是 in 数组下标       for(int i = startIn; i <= endIn;i++){             if(in[i] == pre[startPre]){                 root.left = constructBiTree(pre, startPre+1,startPre+i-startIn, in,startIn,i-1);                 root.right = constructBiTree(pre,startPre+i-startIn+1, endPre,in , i+1, endIn);             }       }       return root;    }        public static void PreOrder(TreeNode root){        if(root != null){            System.out.print(root.val+" ");            PreOrder(root.left);            PreOrder(root.right);        }    }        public static void InOrder(TreeNode root){        if(root != null){            InOrder(root.left);            System.out.print(root.val+" ");            InOrder(root.right);        }    }    /**     * @param args     */    public static void main(String[] args) {        // TODO Auto-generated method stub        /*        int[] a ={1,2,3,4,5,6,7,8};        int[] b = new int[10];        System.arraycopy(a, 0, b, 0, 3);        for(int i = 0; i < b.length ;i++)        System.out.print(b[i]+" ");*/        int[] pre={1,2,4,7,3,5,6,8};        int[] in = {4,7,2,1,5,3,8,6};        TreeNode root = reConstructBinaryTree(pre, in);        PreOrder(root);        System.out.println();        InOrder(root);    }}

重建二叉树：

#include<iostream>#include<stdio.h>#include<cstdlib>#include<cstring>using namespace std;//定义一颗二叉树// BiNode 可以看成二叉树一个节点  *BiTree定义了一个指针变量，　表示树typedef struct BiTNode{    int data;    struct BiTNode *lchild, *rchild;}BiTNode, *BiTree;void  createBiTree(BiTree T){    int ch ;    cin>>ch;    if(ch == 9999){       T = NULL;    }    else{       T = (BiTree)malloc(sizeof(BiTNode));      //申请内存失败 ，报错      if(!T){        cout<<"Get Space Error"<<endl;      }      (T)->data = ch;      createBiTree(T->lchild);      createBiTree(T->rchild);    }}BiTree insert(BiTree root, int  key ){  BiTree p = root;  //新建一个节点 有一个父亲节点  BiTree ptr , pa ;  ptr =(BiTree)malloc(sizeof(BiTNode));  if(ptr==NULL){    cout<<"申请空间失败"<<endl;  }  ptr->rchild = NULL;  ptr->lchild = NULL;  ptr->data = key;  pa = NULL;  if(p == NULL){     return ptr;  }else{      while(p!= NULL){         // 标记当前到哪个点         pa = p;         if(key <= p->data){             p = p->lchild;         }else{             p = p->rchild;         }      }      if(key <= pa->data){         pa->lchild = ptr;      }else{         pa->rchild = ptr ;      }  }  return root ;}BiTree createTree(){ BiTree root = NULL;  int ch ;  cin>>ch;  while(ch != 9999){    root = insert(root, ch);    cin>>ch;  }  return root;}void preOrder(BiTree root){    if(root != NULL){      cout<<root->data<<" ";      preOrder(root->lchild);      preOrder(root->rchild);    }}void inOrder(BiTree root){    if(root!= NULL){       inOrder(root->lchild);       cout<<root->data<<" ";       inOrder(root->rchild);    }}void postOrder(BiTree root){    if(root != NULL){        postOrder(root->lchild);        postOrder(root->rchild);        cout<<root->data<<" ";    }}BiTree constructBiTree(int* startpre , int* endpre, int* startin, int* endin){    int pos;    BiTree root;    int rootValue = startpre[0];    cout<<"rootValue:"<<rootValue<<endl;    root = (BiTree)malloc(sizeof(BiTNode));    root->lchild = NULL;    root->rchild = NULL;    root->data = rootValue;    // 如果只有一个节点    if(startpre== endin){        if(startin == endin && *startin == *endin){            return root;        }else{            cout<<"输入参数有误"<<endl;        }    }    //遍历中序　找到先序节rootvalue 在中序中位置    int *rootIn = startin;    while(rootIn <= endin && *rootIn!=rootValue){           rootIn++;    }    // 将先序数组分成两半    int leftLength = rootIn - startin;    int *leftEndpre = startpre + leftLength;    if(leftLength >0){       root->lchild = constructBiTree(startpre+1, leftEndpre,startin ,rootIn-1);    }    if(leftLength < endpre - startpre){       root->rchild = constructBiTree(leftEndpre+1, endpre, rootIn+1, endin);    }    return root;}BiTree rebuildree(int *pre , int *in ,int  length){    if(pre == NULL || in == NULL || length <=0){        return NULL;    }    return constructBiTree(pre,pre+length-1, in, in+length-1);}int main(){   int pre[] ={1,2,4,7,3,5,6,8};   int in[] ={4,7,2,1,5,3,8,6};   BiTree  root = rebuildree(pre, in,8);//   BiTree root = createTree();   preOrder(root);   cout<<endl;   inOrder(root);   cout<<endl;   postOrder(root);   return 0;}