【HDOJ】2492 Ping pong

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <cstdlib>
 4 
 5 #define MAXN 20005
 6 #define lson l, mid, rt<<1
 7 #define rson mid+1, r, rt<<1|1
 8 
 9 int buf[MAXN], bk[MAXN];
10 int sum[MAXN<<2], n;
11 
12 int comp(const void *a, const void *b) {
13     return *(int *)a - *(int *)b;
14 }
15 
16 void PushUP(int rt) {
17     sum[rt] = sum[rt<<1] + sum[rt<<1|1];
18 }
19 
20 void build(int l, int r, int rt) {
21     sum[rt] = 0;
22     if (l == r)
23         return ;
24     int mid = (l+r)>>1;
25     build(lson);
26     build(rson);
27 }
28 
29 int query(int ll, int rr , int l, int r, int rt) {
30     if (ll<=l && r<=rr)
31         return sum[rt];
32     int mid = (l+r)>>1;
33     int ret = 0;
34     if (ll <= mid)
35         ret += query(ll, rr, lson);
36     if (rr > mid)
37         ret += query(ll, rr, rson);
38     return ret;
39 }
40 
41 void update(int x, int l, int r, int rt) {
42     if (l == r) {
43         ++sum[rt];
44         return ;
45     }
46     int mid = (l+r)>>1;
47     if (x <= mid)
48         update(x, lson);
49     else
50         update(x, rson);
51     PushUP(rt);
52 }
53 
54 int getIndex(int x) {
55     int l=1, r=n, mid;
56 
57     while (l <= r) {
58         mid = (l+r)>>1;
59         if (bk[mid] == x)
60             return mid;
61         if (x > bk[mid])
62             l = mid + 1;
63         else
64             r = mid - 1;
65     }
66     return 0;
67 }
68 
69 int main() {
70     int t;
71     int i;
72     int index;
73     __int64 ll, lg, rl, rg;
74     __int64 ans;
75 
76     scanf("%d", &t);
77     while (t--) {
78         scanf("%d", &n);
79         for (i=1; i<=n; ++i) {
80             scanf("%d", &buf[i]);
81             bk[i] = buf[i];
82         }
83         build(1, n, 1);
84         qsort(bk+1, n, sizeof(int), comp);
85         ans = 0;
86         for (i=1; i<=n; ++i) {
87             index = getIndex(buf[i]);
88             ll = query(1, index, 1, n, 1);
89             lg = i-1-ll;
90             rl = index-1-ll;
91             rg = n-index-lg;
92             ans += ll*rg + lg*rl;
93             update(index, 1, n ,1);
94         }
95         printf("%I64d\n", ans);
96     }
97 
98     return 0;
99 }