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

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。。

 #include<algorithm>

 #include<iostream>

 #include<cstdlib>

 #include<cstring>

 #include<cstdio>

 #include<set>

 using std::max;

 using std::multiset;

 const int Max_N = ;

 typedef unsigned long long ull;

 ull n, p, arr[Max_N];

 void solve() {

     ull res = ;

     multiset<ull> rec;

     for (int i = ; i < n; i++) {

         scanf("%lld", &arr[i]);

         rec.insert(arr[i] %= p);

     }

     multiset<ull>::iterator ite;

     for (int i = ; i < n; i++) {

         rec.erase(rec.find(arr[i]));

         ite = rec.lower_bound(p - arr[i]);

         ull v1 = *--ite;

         ite = rec.lower_bound( * p - arr[i]);

         ull v2 = *--ite;

         res = max(res, max((v1 + arr[i]) % p, (v2 + arr[i]) % p));

         rec.insert(arr[i]);

     }

     printf("%lld\n", res);

 }

 int main() {

 #ifdef LOCAL

     freopen("in.txt", "r", stdin);

     freopen("out.txt", "w+", stdout);

 #endif

     while (~scanf("%lld %lld", &n, &p)) solve();

     return ;

 }

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hdu 5265 pog loves szh II