正文
洛谷 题解 P1351 【联合权值】
小程序:扫一扫查出行
【扫一扫了解最新限行尾号】
复制小程序
【扫一扫了解最新限行尾号】
复制小程序
Problem
P1351 【联合权值】
record
-
用时: 99ms
-
空间: 13068KB(12.76MB)
-
代码长度: 3.96KB
-
提交记录: R9883701
-
注: 使用了
-
o1 优化
-
o2 优化
-
o3 优化
-
use-v4
-
快读快输
Solution
60 or 70 pts
- o1 优化
- o2 优化
- o3 优化
- use-v4
- 快读快输
60 or 70 pts
直接爆搜,枚举每两个距离为 2 的点,然后记录答案。
写法优异可以拿走 70 pts , 但是
use-v4
几乎铁定是 60 pts 。
代码。。。就不放了,有兴趣的可以看:
60 pts(
use-v4
)70 pts(
use-v3
)
70⇒100 pts
考虑我们的思路慢在哪儿?
在于组合!
考虑一个菊花图,复杂度几乎是 Θ(n^2) 的,当然慢。
想到乘法交换律(数学老师不要怪我这么长时间才想起你)
这时候考虑任意两个距离为 2 的有序点对一定会有一个中间点,枚举这个点即可,并不需要搜索。复杂度 Θ(n)Θ(n) ,菊花图不会卡
100 pts
思路基本没什么问题了吧!
等等,图 G 上联合权值的最大值呢?
每次记录中间点相邻点中最大的和次大的即可。
没问题了吧?
不,还有问题!
答案要乘 2 !
因为题目可以看成一对有序点对要计算两次。
Code
// luogu-judger-enable-o2
/*
Problem: P1351 联合权值
Author: 航空信奥
Date: 2018/08/18
Upload: Luogu
P.s.: use-v4
*/
#pragma GCC optimize("O1")
#pragma GCC optimize("O2")
#pragma GCC optimize("O3")
#include <stdio.h>
#include <string.h>
#include <vector>
using namespace std;
namespace AuthorName { /* 防重名 */
template <typename _TpInt> inline _TpInt read();
template <typename _TpInt> inline void write(_TpInt x);
# define Online_Judge
# define Max_N
# define Mod
vector<vector<int> > g;
int *w;
int maxx = , sum = ;
void work(int p)
{
int max_1st = , max_2nd = , temp_sum = ;
for (size_t i = ; i < g[p].size(); i++) {
if (w[g[p][i]] > max_1st) {
max_2nd = max_1st;
max_1st = w[g[p][i]];
}
else if (w[g[p][i]] > max_2nd) {
max_2nd = w[g[p][i]];
}
sum = (sum + temp_sum * w[g[p][i]]) % Mod;
temp_sum = (temp_sum + w[g[p][i]]) % Mod;
}
maxx = max(maxx, max_1st * max_2nd);
}
int main()
{
int n;
n = read<int>();
g.resize(n + );
w = new int[n + ];
int u, v;
for (int i = ; i < n; i++) {
u = read<int>();
v = read<int>();
g[u].push_back(v);
g[v].push_back(u);
}
for (int i = ; i <= n; i++) {
w[i] = read<int>();
}
for (int i = ; i <= n; i++) {
work(i);
}
write(maxx), putchar(), write((sum << ) % Mod), putchar();
return ;
}
#ifdef Online_Judge
char BufferRead[ << ];
int rLen = , rPos = ;
inline char Getchar()
{
if (rPos == rLen) rPos = , rLen = fread(BufferRead, , << , stdin);
if (rPos == rLen) return EOF;
return BufferRead[rPos++];
}
#else
# define Getchar() getchar()
#endif
template <typename _TpInt>
inline _TpInt read()
{
register int flag = ;
register char c = Getchar();
while ((c > '' || c < '') && c != '-')
c = Getchar();
if (c == '-') flag = -, c = Getchar();
register _TpInt init = (c & );
while ((c = Getchar()) <= '' && c >= '')
init = (init << ) + (init << ) + (c & );
return init * flag;
}
template <typename _TpInt>
inline void write(_TpInt x)
{
if (x < ) {
putchar('-');
write<_TpInt>(~x + );
}
else {
if (x > ) write<_TpInt>(x / );
putchar(x % + '');
}
}
}
int main()
{
AuthorName::main();
return ;
}
// luogu-judger-enable-o2
/*
Problem: P1351 联合权值
Author: 航空信奥
Date: 2018/08/18
Upload: Luogu
P.s.: use-v4
*/
#pragma GCC optimize("O1")
#pragma GCC optimize("O2")
#pragma GCC optimize("O3")
#include <stdio.h>
#include <string.h>
#include <vector>
using namespace std; namespace AuthorName { /* 防重名 */
template <typename _TpInt> inline _TpInt read();
template <typename _TpInt> inline void write(_TpInt x); # define Online_Judge
# define Max_N
# define Mod vector<vector<int> > g;
int *w;
int maxx = , sum = ; void work(int p)
{
int max_1st = , max_2nd = , temp_sum = ;
for (size_t i = ; i < g[p].size(); i++) {
if (w[g[p][i]] > max_1st) {
max_2nd = max_1st;
max_1st = w[g[p][i]];
}
else if (w[g[p][i]] > max_2nd) {
max_2nd = w[g[p][i]];
}
sum = (sum + temp_sum * w[g[p][i]]) % Mod;
temp_sum = (temp_sum + w[g[p][i]]) % Mod;
}
maxx = max(maxx, max_1st * max_2nd);
} int main()
{
int n;
n = read<int>();
g.resize(n + );
w = new int[n + ];
int u, v;
for (int i = ; i < n; i++) {
u = read<int>();
v = read<int>();
g[u].push_back(v);
g[v].push_back(u);
}
for (int i = ; i <= n; i++) {
w[i] = read<int>();
}
for (int i = ; i <= n; i++) {
work(i);
} write(maxx), putchar(), write((sum << ) % Mod), putchar(); return ;
} #ifdef Online_Judge
char BufferRead[ << ];
int rLen = , rPos = ;
inline char Getchar()
{
if (rPos == rLen) rPos = , rLen = fread(BufferRead, , << , stdin);
if (rPos == rLen) return EOF;
return BufferRead[rPos++];
}
#else
# define Getchar() getchar()
#endif template <typename _TpInt>
inline _TpInt read()
{
register int flag = ;
register char c = Getchar();
while ((c > '' || c < '') && c != '-')
c = Getchar();
if (c == '-') flag = -, c = Getchar();
register _TpInt init = (c & );
while ((c = Getchar()) <= '' && c >= '')
init = (init << ) + (init << ) + (c & );
return init * flag;
} template <typename _TpInt>
inline void write(_TpInt x)
{
if (x < ) {
putchar('-');
write<_TpInt>(~x + );
}
else {
if (x > ) write<_TpInt>(x / );
putchar(x % + '');
}
}
} int main()
{
AuthorName::main();
return ;
}