逆序数 UVALive 6508 Permutation Graphs

 1 /*
 2     题意：给了两行的数字，相同的数字连线，问中间交点的个数
 3     逆序数：第一行保存每个数字的位置，第二行保存该数字在第一行的位置，接下来就是对它求逆序数
 4         用归并排序或线段树求。想到了就简单了:)
 5 */
 6 #include <cstdio>
 7 #include <algorithm>
 8 #include <cstring>
 9 #include <cmath>
10 #include <vector>
11 using namespace std;
12 
13 typedef long long ll;
14 const int MAXN = 1e5 + 10;
15 const int INF = 0x3f3f3f3f;
16 int p[MAXN], a[MAXN];
17 int L[MAXN/2+10], R[MAXN/2+10];
18 ll ans;
19 
20 void Merge(int *a, int p, int q, int r)
21 {
22     int n1 = q - p + 1, n2 = r - q;
23     for (int i=1; i<=n1; ++i)    L[i] = a[p+i-1];
24     for (int i=1; i<=n2; ++i)    R[i] = a[q+i];
25     L[n1+1] = INF;    R[n2+1] = INF;
26 
27     int i = 1, j = 1;
28     for (int k=p; k<=r; ++k)
29     {
30         if (L[i] <= R[j])    a[k] = L[i++];
31         else    {a[k] = R[j++];    ans += n1 - i + 1;}
32     }
33 }
34 
35 void MergeSort(int *a, int p, int r)
36 {
37     if (p < r)
38     {
39         int q = (p + r) / 2;
40         MergeSort (a, p, q);
41         MergeSort (a, q + 1, r);
42         Merge (a, p, q, r);
43     }
44 }
45 
46 int main(void)        //UVALive 6508 Permutation Graphs
47 {
48 //    freopen ("I.in", "r", stdin);
49 
50     int t;    scanf ("%d", &t);
51     while (t--)
52     {
53         int n;    scanf ("%d", &n);
54         for (int i=1; i<=n; ++i)
55         {
56             int x;    scanf ("%d", &x);    p[x] = i;
57         }
58         for (int i=1; i<=n; ++i)
59         {
60             int x;    scanf ("%d", &x);    a[i] = p[x];
61         }
62 
63         ans = 0;
64         MergeSort (a, 1, n);
65         printf ("%lld\n", ans);
66     }
67 
68     return 0;
69 }