【CDOJ931】Car race game（树状数组求逆序）

题目连接：http://acm.uestc.edu.cn/#/problem/show/931

OJ评判系统有些坑，不支持__int64以及输出的%I64d大家注意。全开long long也会TLE，比较坑。逆序的基础操作题，不错。

 #include <bits/stdc++.h>
 #define MAX 100010
 using namespace std;

 int s[MAX * ];

 struct Node {
     int x, v;
 } node[MAX];

 bool cmp (Node a, Node b) {
     if (a.x == b.x) {
         return a.v > b.v;
     }
     return a.x < b.x;
 }

 int lowbit (int x) {
     return x & (-x);
 }

 int sum (int p) {
     int ans = ;
     while (p) {
         ans += s[p];
         p -= lowbit(p);
     }
     return ans;
 }

 void add (int p, int del) {
     while (p <= ) {
         s[p] += del;
         p += lowbit(p);
     }
 }

 int main () {
     int n, i;
     while (scanf("%d", &n) != EOF) {
         long long ans = ;
         for (i = ; i < n; ++ i) {
             scanf("%d %d", &node[i].x, &node[i].v);
         }
         sort (node, node + n, cmp);
         memset(s, , sizeof(s));
         for (i = ; i < n; ++ i) {
             ans = ans + i - sum(node[i].v);
             add(node[i].v, );
         }
         printf ("%lld\n", ans);
     }
     return ;
 }