poj2255树的重建问题

#include<iostream>

#include<cstring>

#include<cstdlib>

#include<cstdio>

#include<string>

#include<sstream>

#include<vector>

using namespace std;

const int maxn = 30;

struct node {
int left;
int right;
char value;
node() {
left = -1;
right = -1;
}

};

string pre, in;

node tree[maxn];

int root = 0;

int cnt = 0;

vector<char> ans;

int index = 0;

int build(int l,int r)

{
if (l > r)return -1;

char ch = pre[cnt++];
int pos = 0;
for (int i = l; i <= r; i++)
{
if (in[i] == ch)
{
pos = i; break;
}
}
tree[index].value = ch;
tree[index].left = build(l, pos - 1);
tree[index].right = build(pos + 1, r);
ans.push_back(ch);

return index++;

}

int main()

{
//freopen("input.txt","r",stdin);

while (cin >> pre) {
cin >> in;
root = 0;
cnt = 0;
index = 0;
for (int i = 0; i < maxn; i++)tree[i].left = -1, tree[i].right = -1;
ans.clear();

root = build(0, pre.length()-1);

for (int i = 0; i < ans.size(); i++)
cout << ans[i];
cout << endl;
}
return 0;

}