hdu 5481 Desiderium(高效)

代码

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;
typedef pair<int,int> pii;
typedef long long ll;
const int maxn = 1e5 + 5;
const int mod = 1e9 + 7;

int N, P[maxn];
vector<pii> G;

void init () {
int l, r;
scanf("%d", &N);
G.clear();

for (int i = 1; i <= N; i++) {
scanf("%d%d", &l, &r);
G.push_back(make_pair(l, 1));
G.push_back(make_pair(r, -1));
}
sort(G.begin(), G.end());
}

int solve () {
int c = 0, p = 0, n = G.size(), ret = 0;
while (p < n) {
c += G[p++].second;
while (p < n && G[p].first == G[p-1].first)
c += G[p++].second;
if (p == n) break;

int len = G[p].first - G[p-1].first;
ret = (ret + 1LL * len * (P[c]-1) % mod * P[N-c] % mod) % mod;
}
return ret;
}

int main () {
P[0] = 1;
for (int i = 1; i < maxn; i++) P[i] = P[i-1] * 2 % mod;

int cas;
scanf("%d", &cas);
while (cas--) {
init();
printf("%d\n", solve());
}
return 0;
}