1 #include <bits/stdc++.h> 2 #define _for(i,a,b) for(int i = (a);i < b;i ++) 3 typedef long long ll; 4 using namespace std; 5 string S; 6 int N; 7 inline ll read() 8 { 9 ll ans = 0; 10 char ch = getchar(), last = ' '; 11 while(!isdigit(ch)) last = ch, ch = getchar(); 12 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar(); 13 if(last == '-') ans = -ans; 14 return ans; 15 } 16 inline void write(ll x) 17 { 18 if(x < 0) x = -x, putchar('-'); 19 if(x >= 10) write(x / 10); 20 putchar(x % 10 + '0'); 21 } 22 struct TreeNode 23 { 24 char val; 25 TreeNode *left; 26 TreeNode *right; 27 }; 28 char judge(int le,int ri) 29 { 30 bool oflag = false; 31 bool zflag = false; 32 _for(i,le,ri+1) 33 { 34 if(S[i]=='0') 35 zflag = true; 36 else if(S[i]=='1') 37 oflag = true; 38 } 39 if(zflag && !oflag) 40 return 'B'; 41 else if(!zflag && oflag) 42 return 'I'; 43 else 44 return 'F'; 45 return -1; 46 } 47 TreeNode* build(int le,int ri) 48 { 49 TreeNode* tmp = (TreeNode*)malloc(sizeof(TreeNode)); 50 int mi = (le+ri)/2; 51 tmp->val = judge(le,ri); 52 if(le!=ri) 53 { 54 tmp->left = build(le,mi); 55 tmp->right = build(mi+1,ri); 56 } 57 else 58 tmp->left = tmp->right = NULL; 59 return tmp; 60 } 61 void postorder(TreeNode *root) 62 { 63 if(!root) 64 return ; 65 postorder(root->left); 66 postorder(root->right); 67 printf("%c",root->val); 68 } 69 int main() 70 { 71 TreeNode* root; 72 scanf("%d",&N); 73 cin >> S; 74 root = build(0,pow(2,N)-1); 75 postorder(root); 76 return 0; 77 }