PKU 3067 Japan 樹狀數組

求道路的交叉點數。

將道路按左邊城市從大到小排序。如果相同則按右邊從大到小排序。

這樣就跟stars和cows一樣了。

#include <iostream>#include <algorithm>using namespace std;const int maxn = 1010;int c[maxn],result[maxn];typedef struct{int e, s;} node;node nd[maxn * maxn];bool cmp(node a , node b){if(a.s == b.s)return a.e > b.e;return a.s > b.s;}int Lowbit(int x)  {  return x & (-x);  }  void Update(int x) {int i;for(i = x; i < maxn; i += Lowbit(i)){c[i]++;}}int Getsum(int x)  {  long long sum = 0;  int i;for( i = x; i > 0; i -= Lowbit(i) )  {  sum += c[i];}  return sum;  }  int main(){int t;scanf("%d", &t);for(int cas = 1; cas <= t; cas++){int l, r;int n;scanf("%d%d%d", &l, &r, &n);memset(c, 0, sizeof(c)); memset(result, 0, sizeof(result));int x, y;for(int i = 1; i <= n; i++){scanf("%d %d", &x, &y);nd[i].s = x + 1;nd[i].e = y + 1; }sort(nd+1, nd+n+1, cmp);long long  sum = 0;for(int i = 1; i <= n; i ++){sum += Getsum(nd[i].e - 1); //注意這裡要減1Update(nd[i].e);}printf("Test case %d: %lld\n", cas, sum);}return 0;}