0ms,这题要注意两点,一是节点数据可能为负,二是输入时使用cin.unget()可让输入流退回上一格,神奇啊!

http://acm.pku.edu.cn/JudgeOnline/problem?id=1145

#include <iostream>
#define MAX_N 10000
using namespace std;
struct node
{
 int sum;
 node *lchild;
 node *rchild;
};
node freeNode[MAX_N];
int p,target;
bool Done;

bool getNext(int &data,char &ch)
{
 data=-1;
 ch=' ';
 while(ch==' ')
  cin>>ch;
 if(ch>='0'&&ch<='9'||ch=='-')
 {
  cin.unget();
  cin>>data;
  return false;
 }
 return true;
}

node *build(int sum)
{
 char ch;
 int data;
 bool isCh;
 isCh=getNext(data,ch);
 isCh=getNext(data,ch);
 if(isCh&&ch==')'||ch=='\n')
  return NULL;
 node *newNode=&freeNode[p++];
 newNode->sum=data+sum;
 newNode->lchild=build(newNode->sum);
 newNode->rchild=build(newNode->sum);
    if(newNode->lchild==NULL&&newNode->rchild==NULL&&newNode->sum==target)
  Done=true;
 isCh=getNext(data,ch);
 return newNode;
}

int main()
{
 while(scanf("%d",&target)!=EOF)
 {
  p=0,Done=false;
  node *root=build(0);
  if(Done)
   printf("yes\n");
  else
   printf("no\n");
 }
 return 0;
}