题目连接
http://acm.hdu.edu.cn/showproblem.php?pid=5265
pog loves szh II
Description
Pog and Szh are playing games.There is a sequence with n numbers, Pog will choose a number A from the sequence. Szh will choose an another number named B from the rest in the sequence. Then the score will be $(A+B)$ mod $p.$They hope to get the largest score.And what is the largest score?
Input
Several groups of data (no more than 5 groups,$n geq 1000$).
For each case:
The following line contains two integers,$n(2 leq n leq 100000)，p(1 leq p leq 2^{31}-1)$。
The following line contains $n$ integers $a_i(0 leq a_i leq 2^{31}-1)$。
Output
For each case,output an integer means the largest score.
Sample Input
4 4
1 2 3 0
4 4
0 0 2 2
Sample Output
3
2
原先用二分写挂了，估计边界没处理好，换了set好歹过了，罪过，罪过。。
1 #include<algorithm> 2 #include<iostream> 3 #include<cstdlib> 4 #include<cstring> 5 #include<cstdio> 6 #include<set> 7 using std::max; 8 using std::multiset; 9 const int Max_N = 100010; 10 typedef unsigned long long ull; 11 ull n, p, arr[Max_N]; 12 void solve() { 13 ull res = 0; 14 multiset<ull> rec; 15 for (int i = 0; i < n; i++) { 16 scanf("%lld", &arr[i]); 17 rec.insert(arr[i] %= p); 18 } 19 multiset<ull>::iterator ite; 20 for (int i = 0; i < n; i++) { 21 rec.erase(rec.find(arr[i])); 22 ite = rec.lower_bound(p - arr[i]); 23 ull v1 = *--ite; 24 ite = rec.lower_bound(2 * p - arr[i]); 25 ull v2 = *--ite; 26 res = max(res, max((v1 + arr[i]) % p, (v2 + arr[i]) % p)); 27 rec.insert(arr[i]); 28 } 29 printf("%lld ", res); 30 } 31 int main() { 32 #ifdef LOCAL 33 freopen("in.txt", "r", stdin); 34 freopen("out.txt", "w+", stdout); 35 #endif 36 while (~scanf("%lld %lld", &n, &p)) solve(); 37 return 0; 38 }