NOIP 2004 普及组 sdnu 1168.FBI树

#include<iostream>
#include<cmath>
#include<string>
#include<cstring>
using namespace std;
typedef struct node
{
char fbi;
struct node * leftchild, *rightchild;
node() :leftchild(NULL), rightchild(NULL){}		//构造函数的简写
}*NODE;

string numstr;

void CreatFbiTree(int left,int right,NODE parent)
{
if (left == right)		//递归结束条件
{
if (numstr[left] == '0')
parent->fbi = 'B';
else parent->fbi = 'I';
return;
}
bool b = false, i = false;			//判断0，1
for (int j = left; j <= right; j++)
{
if (numstr[j] == '0'&&!b)
b = true;
else if (numstr[j] == '1'&&!i)
i = true;
if (i&&b) break;
}
if (i&&b)		parent->fbi = 'F';
else if (!i&&b)		parent->fbi = 'B';
else	parent->fbi = 'I';
if (left <= (right + left) / 2)
{
parent->leftchild = new node();
CreatFbiTree(left, (right + left) / 2, parent->leftchild);
}
if ((right + left) / 2 + 1 <= right)
{
parent->rightchild = new node();
CreatFbiTree((right + left) / 2 + 1, right, parent->rightchild);
}
return;
}
void PostTraverseTree(NODE root)		//后序遍历
{
if (NULL != root->leftchild)
PostTraverseTree(root->leftchild);
if (NULL != root->rightchild)
PostTraverseTree(root->rightchild);
cout << root->fbi;
return;
}
int main()
{
int n;
cin >> n;
NODE root=new node();
cin >> numstr;
CreatFbiTree(0, numstr.length() - 1, root);
PostTraverseTree(root);
cout << endl;
return 0;
}