实现由先序、中序序列构造二叉树的算法，实现由后序、中序序列构造二叉树的算法

一道上机题 思想是递归

如果不理解原理可以看这个博客 注释里的说明很详细：http://blog.csdn.net/yunzhongguwu005/article/details/9270085

在代码的注释部分有测试样例

先序和中序：

#include<algorithm>#include<iostream>#include<cstdlib>#include<cstring>#include<cstdio>#include<string>#include<stack>#include<queue>#include<cmath>#include<stack>#include<list>#include<map>#include<set>#define up(i,x,y) for(i=x;i<=y;i++)#define down(i,x,y) for(i=x;i>=y;i--)#define mem(a,x) memset(a,x,sizeof(a))#define gi(x) scanf("%d",&x)#define gi2(x,y) scanf("%d%d",&x,&y)#define gll(x) scanf("%lld",&x)#define gll2(x,y) scanf("%lld%lld",&x,&y)#define gc(x) scanf("%c",&x)#define gc2(x,y) scanf("%c%c",&x,&y)using namespace std;const double eps=1e-8; typedef long long ll;const int MAXN=100005;const int mod=1000000007;const ll llinf = (ll)(1e18) + 500;const int inf=0x3f3f3f3f;struct Node{char c;Node *lson;Node *rson;};void build(Node* &t,string prestr,string instr){if(prestr.size()==0){t=NULL;return;}char rootch=prestr[0];int index=instr.find(rootch);//下标string lsoninstr=instr.substr(0,index);string rsoninstr=instr.substr(index+1);int lsonlen=lsoninstr.size();//int rsonlen=rsoninstr.size();string lsonprestr=prestr.substr(1,lsonlen);string rsonprestr=prestr.substr(lsonlen+1);t=new Node;if(t){t->c=rootch;build(t->lson, lsonprestr, lsoninstr);build(t->rson, rsonprestr, rsoninstr);}}void preorderTraverse(Node* & t)   {    if(t!=NULL)    {  cout<<t->c;  preorderTraverse(t->lson);  preorderTraverse(t->rson);    }   }  void inorderTraverse(Node* & t)   {    if(t!=NULL)    {  inorderTraverse(t->lson);cout<<t->c;  inorderTraverse(t->rson);    }   } void postorderTraverse(Node* & t)   {    if(t!=NULL)    {  postorderTraverse(t->lson); postorderTraverse(t->rson);  cout<<t->c;   }   }  //string pre = "1234567";//string in = "3241657";//后序 3 4 2 6 7 5 1 int main(){int i,j,k;string prestr,instr;//prestr="ABCDEFG";//instr="CBEDAFG";prestr="1234567";instr="3241657";Node *root;build(root,prestr,instr);preorderTraverse(root);cout<<endl;inorderTraverse(root);cout<<endl;postorderTraverse(root);cout<<endl;return 0;}

中序和后序：

#include<algorithm>#include<iostream>#include<cstdlib>#include<cstring>#include<cstdio>#include<string>#include<stack>#include<queue>#include<cmath>#include<stack>#include<list>#include<map>#include<set>#define up(i,x,y) for(i=x;i<=y;i++)#define down(i,x,y) for(i=x;i>=y;i--)#define mem(a,x) memset(a,x,sizeof(a))#define gi(x) scanf("%d",&x)#define gi2(x,y) scanf("%d%d",&x,&y)#define gll(x) scanf("%lld",&x)#define gll2(x,y) scanf("%lld%lld",&x,&y)#define gc(x) scanf("%c",&x)#define gc2(x,y) scanf("%c%c",&x,&y)using namespace std;const double eps=1e-8; typedef long long ll;const int MAXN=100005;const int mod=1000000007;const ll llinf = (ll)(1e18) + 500;const int inf=0x3f3f3f3f;struct Node{char c;Node *lson;Node *rson;};void build(Node* &t,string poststr,string instr){if(poststr.size()==0){t=NULL;return;}char rootch=poststr[poststr.size()-1];int index=instr.find(rootch);//下标string lsoninstr=instr.substr(0,index);string rsoninstr=instr.substr(index+1);int lsonlen=lsoninstr.size();int rsonlen=rsoninstr.size();string lsonpoststr=poststr.substr(0,lsonlen);string rsonpoststr=poststr.substr(lsonlen,poststr.size()-1-lsonlen);//string rsonpoststr=rsonpoststrtmp.substr(0,);t=new Node;if(t){t->c=rootch;build(t->lson, lsonpoststr, lsoninstr);build(t->rson, rsonpoststr, rsoninstr);}}void preorderTraverse(Node* & t)   {    if(t!=NULL)    {  cout<<t->c;  preorderTraverse(t->lson);  preorderTraverse(t->rson);    }  }  void inorderTraverse(Node* & t)   {    if(t!=NULL)    {  inorderTraverse(t->lson);cout<<t->c;  inorderTraverse(t->rson);    }   } void postorderTraverse(Node* & t)   {    if(t!=NULL)    {  postorderTraverse(t->lson); postorderTraverse(t->rson);  cout<<t->c;   }   } //string pre = "1234567";//string in = "3241657";//后序 3 4 2 6 7 5 1 int main(){int i,j,k;string poststr,instr;//prestr="ABCDEFG";//instr="CBEDAFG";poststr="3426751";instr="3241657";Node *root;build(root,poststr,instr);preorderTraverse(root);cout<<endl;inorderTraverse(root);cout<<endl;postorderTraverse(root);cout<<endl;return 0;}