DFS+剪枝 HDOJ 5323 Solve this interesting problem

题目传送门

 /*
     题意：告诉一个区间[L,R]，问根节点的n是多少
     DFS+剪枝：父亲节点有四种情况：[l, r + len],[l, r + len - 1],[l - len, r],[l - len -1,r];
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #include <queue>
 using namespace std;

 typedef long long ll;
 const int INF = 0x3f3f3f3f;
 const ll INFL = 1e30;
 ll ans;

 void DFS(ll l, ll r)  {
     if (l > r || l < ) return ;
     if (l == ) {
         ans = min (ans, r); return ;
     }
     ll len = r - l + ;
     if (l < len)    return ;
     DFS (l, r + len);
     if (len != )   DFS (l, r + len - );
     DFS (l - len, r);   DFS (l - len - , r);
 }

 int main(void)  {       //HDOJ 5323 Solve this interesting problem
     //freopen ("H.in", "r", stdin);

     ll L, R;
     while (scanf ("%I64d%I64d", &L, &R) == ) {
         if (L == )   {
             if (R >= L) printf ("%I64d\n", R);
             else    puts ("-1");
             continue;
         }
         ans = INFL; DFS (L, R);
         printf ("%I64d\n", (ans == INFL) ? - : ans);
     }

     return ;
 }