poj 3067 Japan

题意：日本东海岸有n个城市，西海岸有m个城市，现在要修建k条高铁连接东海岸的城市u和西海岸的城市v。问这k条高铁总共有多少个交点。

思路：树状数组。（本人未理解，装载供以后学习）

代码：

#include <iostream>#include <algorithm>#include <cstdio>using namespace std;const int MAX = 1009;typedef long long ll;ll arr[MAX];int n,m,k;struct way{int e,w;}w[MAX*MAX];int lowbit(int k){return k&(-k);}void modify(int num){while(num <= m){arr[num] += 1;num += lowbit(num);}}ll sum(int num){ll ans = 0;while(num > 0){ans += arr[num];num -= lowbit(num);}return ans;}int cmp(way a, way b){if(a.e == b.e)return a.w > b.w;return a.e > b.e;}int main(void){int test;int c=0;scanf("%d",&test);while(test--){memset(arr,0,sizeof(arr));scanf("%d%d%d",&n,&m,&k);int i;for(i=0; i<k; i++)scanf("%d%d",&w[i].e,&w[i].w);sort(w,w+k,cmp);ll ans = 0;for(i=0; i<k; i++){ans += sum(w[i].w-1);modify(w[i].w);}printf("Test case %d: %lld/n",++c,ans);}return 0;}