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 < 0) return ;
    if (l == 0) {
        ans = min (ans, r); return ;
    }
    ll len = r - l + 1;
    if (l < len)    return ;
    DFS (l, r + len);
    if (len != 1)   DFS (l, r + len - 1);
    DFS (l - len, r);   DFS (l - len - 1, r);
}

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

    ll L, R;
    while (scanf ("%I64d%I64d", &L, &R) == 2) {
        if (L == 0)   {
            if (R >= L) printf ("%I64d
", R);
            else    puts ("-1");
            continue;
        }
        ans = INFL; DFS (L, R);
        printf ("%I64d
", (ans == INFL) ? -1 : ans);
    }

    return 0;
}