fzu 1962 树状数组

优雅的树状数组！人们发明了复杂度为logn的求解第k小的方法，常数小且代码量小，实在是用来求解本类题目的最佳方法，可惜的是我的Treap超时了......

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdio>
 4 using namespace std;
 5
 6 const int N = 500001;
 7 int c[N];
 8 int n, m, maxn;
 9
10 int lb( int i )
11 {
12     return i & -i;
13 }
14
15 void update( int i, int v )
16 {
17     while ( i <= n )
18     {
19         c[i] += v;
20         i += lb(i);
21     }
22 }
23
24 int sum( int i )
25 {
26     int ans = 0;
27     while ( i )
28     {
29         ans += c[i];
30         i -= lb(i);
31     }
32     return ans;
33 }
34
35 int kth( int k )
36 {
37     int ans = 0, cnt = 0;
38     for ( int i = 20; i >= 0; i-- )
39     {
40         ans += ( 1 << i );
41         if ( ans >= maxn || cnt + c[ans] >= k )
42         {
43             ans -= ( 1 << i );
44         }
45         else
46         {
47             cnt += c[ans];
48         }
49     }
50     return ans + 1;
51 }
52
53 int main ()
54 {
55     while ( scanf("%d%d", &n, &m) != EOF )
56     {
57         memset( c, 0, sizeof(c) );
58         for ( int i = 1; i <= n; i++ )
59         {
60             update( i, 1 );
61         }
62         maxn = n;
63         while ( m-- )
64         {
65             char op[2];
66             int num;
67             scanf("%s%d", op, &num);
68             if ( op[0] == ‘L‘ )
69             {
70                 int kk = kth(num);
71                 update( kk, -1 );
72             }
73             else if ( op[0] == ‘R‘ )
74             {
75                 if ( sum(num) == sum( num - 1 ) )
76                 {
77                     update( num, 1 );
78                 }
79             }
80             else if ( op[0] == ‘Q‘ )
81             {
82                 int kk = kth(num);
83                 printf("%d\n", kk);
84             }
85         }
86     }
87     return 0;
88 }