poj3067 树状数组(Binary Indexed Tree)

题意:所有线段的出发于右边（from)，终止于左边(to)，求线段交点的个数
思路：(1)线段有交点,则fromj>fromi&&toi<toj或fromj<fromi&&toj>toi;
     (2)定义结构体struct cnode{int from,int to}node[MAXN];可将每个结点的to值取负再加1001，则只需满足fromj>fromi&&toj>toi
     （3）按from从小到大排，如果from相等，则按to从大到小排,用树状数组保存to区间的和，则
     from i:=1  to n(n个结点）
     {
        sum(node[i].to-1);//同一个出发点的不算
    insert(node[i].to);
     }

代码：

#include <iostream> #include <cstdio> #include <cstring> #include <algorithm> using namespace std; const int MAXN=1000000; struct cnode { int from; int to; }node[MAXN+10]; bool cmp(const cnode &e1,const cnode &e2) { if(e1.from!=e2.from) { return e1.from<e2.from? true:false; } else { return e1.to>e2.to? true:false; } } int tree[1010]; int sum(int x) { int value=0; while(x>0) { value+=tree[x]; x-=(x&(x^(x-1))); } return value; } void insert(int x) { while(x<=1000) { tree[x]++; x+=(x&(x^(x-1))); } } int main() { int t; int Case; int N,M,K; int i; long long ans; scanf("%d",&t); for(Case=1;Case<=t;Case ++) { memset(tree,0,sizeof(tree)); scanf("%d %d %d",&N,&M,&K); for(i=1;i<=K;i++) { scanf("%d %d",&node[i].from,&node[i].to); node[i].to=-node[i].to+1001; } sort(&node[0],&node[K+1],cmp); ans=0; for(i=1;i<=K;i++) { ans+=sum(node[i].to-1); // cout<<"ans: "<<ans<<endl; insert(node[i].to); } printf("Test case %d: %lld/n",Case,ans); } return 0; }

题目：
Japan
Time Limit: 1000MS        Memory Limit: 65536K
Total Submissions: 10870        Accepted: 2886

Description
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

Source
Southeastern Europe 2006