POJ - 3067

第二天叫醒我的不是闹钟，是梦想!

Japan plans to welcome the ACM ICPC World Finals and a lot of roads must be built for the venue. Japan is tall island with N cities on the East coast and M cities on the West coast (M <= 1000, N <= 1000). K superhighways will be build. Cities on each coast are numbered 1, 2, … from North to South. Each superhighway is straight line and connects city on the East coast with city of the West coast. The funding for the construction is guaranteed by ACM. A major portion of the sum is determined by the number of crossings between superhighways. At most two superhighways cross at one location. Write a program that calculates the number of the crossings between superhighways.
Input
The input file starts with T - the number of test cases. Each test case starts with three numbers – N, M, K. Each of the next K lines contains two numbers – the numbers of cities connected by the superhighway. The first one is the number of the city on the East coast and second one is the number of the city of the West coast.
Output
For each test case write one line on the standard output:
Test case (case number): (number of crossings)
Sample Input
1
3 4 4
1 4
2 3
3 2
3 1
Sample Output
Test case 1: 5

树状数组:先排序，再求逆序数

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
const int N=1e6+10;
const int maxn=1015;
int n,m,k,t;
int vis[N];
int c[N];
typedef long long ll;
struct node
{int a,b;
}a[N];
int lowbit(int x)
{return x&(-x);
}
void add(int i,int x)
{while(i<=maxn){c[i]+=x;i+=lowbit(i);}
}
int sum(int i)
{int res=0;while(i>0){res+=c[i];i-=lowbit(i);}return res;
}bool cmp(const node &a,const node &b)
{if(a.b==b.b) return a.a<b.a;return a.b<b.b;
}
int main()
{scanf("%d",&t);int p=0;while(t--){memset(c,0,sizeof c);cin>>n>>m>>k;for(int i=1;i<=k;i++){scanf("%d %d",&a[i].a,&a[i].b);}sort(a+1,a+1+k,cmp);ll ans=0;for(int i=1;i<=k;i++){ans=ans+sum(maxn)-sum(a[i].a);add(a[i].a,1);}printf("Test case %d: %lld\n",++p,ans);}return 0;
}

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