uva 100 The 3n + 1 problem (RMQ)

uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=36

　　预处理，RMQ求区间最大值。

代码如下：

 #include <cstdio>
 #include <iostream>
 #include <cstring>
 #include <algorithm>
 #include <cmath>

 using namespace std;

 typedef long long LL;
 const int N = ;
 const int M = ;
 int pre[N], RMQ[M][N >> ];
 int dfs(LL n) {
     if (n <= ) cout << n << endl;
     if (n < N && pre[n]) return pre[n];
     int tmp;
     if (n & ) tmp = dfs(n *  + ) + ;
     else tmp = dfs(n >> ) + ;
     if (n < N) pre[n] = tmp;
     return tmp;
 }

 void PRE() {
     pre[] = ;
     for (int i = , end = N >> ; i < end; i++) if (pre[i] == ) dfs(i);
 //    for (int i = 1; i < 20; i++) cout << i << ' ' << pre[i] << endl;
     // prepare RMQ
     for (int i = , end = N >> ; i < end; i++) RMQ[][i] = pre[i];
     for (int i = ; i < M; i++) {
         for (int j = , end = (N >> ) - ( << i); j <= end; j++) {
             RMQ[i][j] = max(RMQ[i - ][j], RMQ[i - ][j + ( << i - )]);
         }
     }
 }

 int query(int l, int r) {
     if (l > r) swap(l, r);
     int ep = (int) log2((double) r - l + );
     return max(RMQ[ep][l], RMQ[ep][r - ( << ep) + ]);
 }

 int main() {
     PRE();
     int l, r;
     while (cin >> l >> r) cout << l << ' ' << r << ' ' << query(l, r) << endl;
     return ;
 }

——written by Lyon