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江山代有才人出,各领风骚数百年

2021-03-04 17:45:17 By SocietyNiu

这段时间学习函数的递归,猛然发现自己连dfs和bfs都忘得精光,想在洛谷上找些题练手,突然想起lfyzoj,万幸,自己的号还在,索性写点东西,留于后人谈。

我是SocietyNiu,2017年接触oi,2018年参加noip,只拿了个省三,现zju金融大一,可能是为数不多的文科oier。(不知道有没有学弟学妹oier选了文)

就目前的强基计划等招生模式而言,在山西临汾这样一个相对教育弱省,想要通过奥赛直接获得大学入学门票,是一件不容易的事,但是学习oi绝不仅仅是为了那一纸证书。学习oi对我来说是一个正确的选择,它虽然没有给我带来升学、招生等各方面的优惠,但在其他方面oi确实让我受益匪浅。算法的学习和C语言的掌握,使我能够快速入手其他编程语言,编写爬虫或其他小程序,也让我逐渐养成了超越一般文科生的逻辑思维,功利点来说,它也使我大一上的C语言程序设计课程取得了不错的成绩。

其实这是一篇怀旧贴,每当想起oi,总能想起许许多多

想起北京昌平军都大酒店(qbxt)
想起觍着脸向班主任请求停课
想起机房里欢乐的笑声
想起图书艺术楼5层厕所出去天台上俯瞰学校的美景
想起全校只有oier提前开学的那段日子
想起与@luv_letters @RiverSTARSKy @goddess_Q @KearTnT等队友并肩作战的时光

物是人非,洛谷的团队已不见更新,oier老人奔赴全国各地,老韩也去追逐自己的信仰。

“江山代有才人出,各领风骚数百年。”希望学弟学妹再接再励,文化课与oi成绩齐头并进!

最后,感谢lfyzoj的运营组与维护组。

如果有文科方面的问题或想来zju念书,欢迎向我询问,我的vx是:a962271992

关于#242的SPJ

2018-09-28 17:14:18 By SocietyNiu

请问#242是不是有多组解? 例如样例

300 250 275 252 200 138 245

$O(nlogn)$算法算出来的是

138 245

高一T2真题解

2018-08-28 13:31:25 By SocietyNiu

由于我的失误,题解放早了十几分钟,导致有些同学抄袭,在这里我不再追究,请大家弄清楚题解后自己打一遍,本身题目不难。 还有考试时没有网,导致markdown的图例没有显示,对大家说一句抱歉

首先要了解:^运算符优先级低于==

知道这个,其实已经50分到手了(是不是特别水)

//50分代码
#include<iostream>
using namespace std;
int main()
{
    int n;
    cin>>n;
    int sum=0;
    for(int i=1;i<=n;i++)
     for(int j=1;j<=i;j++)
      for(int k=1;k<=j;k++)
        if((i^j^k)==0)//```^```运算符优先级低于```==```,所以要加i^j^k括号
         if(i+j>k&&i+k>j&&k+j>i)
            sum++;
    cout<<sum;
}

可是这个方法时间复杂度为O(n^3),过不了2500以上的数据。这时就要优化

假设我只枚举a和b,那么如何求c呢?

首先我们要推出异或的一个运算法则,a^b^c=(a^b)^c

知道这个后,我们就可以进行胡搞推导.

题目要求a^b^c==0,即(a^b)^c==0,根据异或的运算法则可知(a^b)c按位相等,二进制上每一位都是一样的,所以(a^b)==c

这时候就可以枚举了啊(属实不难啊)

代码如下

#include<iostream>
using namespace std;
int main()
{
    int n;
    cin>>n;
    int sum=0;
    for(int i=1;i<=n;i++)
     for(int j=1;j<=i;j++)
     {
       int k=(i^j);
       if(i+j>k&&i-j<k)
           if(k<j&&k<i)
         sum++;
     }
    cout<<sum;
}

热烈欢迎高一选手吊打高二oier

2018-08-15 08:22:17 By SocietyNiu

重要通知of停课

2018-06-15 17:45:36 By SocietyNiu

全体信息竞赛生周二 上午8点30到12点 下午2点30到6点 进行全真模拟赛,晚上讲题、安排暑假事宜

(意味着你们要请一天的假)

不来小心AFO

建议修改输出样例

2018-03-07 18:37:17 By SocietyNiu

http://lfyzit.com/problem/92

N皇后问题的问题

输出格式中写到“一行中每个数字占5个宽度且靠右”;

output却是“2 4 1 3”

建议更正

#73. 最少步数 简单又粗暴

2018-02-24 01:50:57 By SocietyNiu

你懂得打表出奇迹的神奇吗???

(仅供娱乐,下方有普通代码)

#include<iostream>
using namespace std;
int a[100][100]={2,2,2,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,2,3,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,2,1,1,3,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,2,2,3,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,2,2,2,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,3,3,3,3,3,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,3,3,3,3,3,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,4,4,4,4,4,4,4,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,4,4,4,4,4,4,4,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,5,5,5,5,5,5,5,5,5,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,5,5,5,5,5,5,5,5,5,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,6,6,6,6,6,6,6,6,6,6,6,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,6,6,6,6,6,6,6,6,6,6,6,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,38,39,39,40,40,41,41,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,25,25,26,26,27,27,28,28,29,29,30,30,31,31,32,32,33,33,34,34,35,35,36,36,37,37,38,3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2,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,44,44,45,45,46,46,47,47,48,48,49,49,50,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,45,45,46,46,47,47,48,48,49,49,50,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,44,45,45,46,46,47,47,48,48,49,49,50,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,46,46,47,47,48,48,49,49,50,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,45,46,46,47,47,48,48,49,49,50,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,47,47,48,48,49,49,50,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,46,47,47,48,48,49,49,50,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,48,48,49,49,50,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,47,48,48,49,49,50,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,49,49,50,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,48,49,49,50,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,50,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,49,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50,50};
int main()
{
    for(int i=1;i<=2;i++)
    {
        int x,y;cin>>x>>y;
        cout<<a[x-1][y-1]<<endl;
    }
    return 0;
}

普通代码及讲解

注意:讲解来自于《信息学奥赛一本通》

讲解部分:

由于A、B两点是随机输入的,因此无法找到计算最少步数的数学规律,只能通过广度优先搜索的办法求解。

1、确定出发点 从(x,y)出发通过一次广度优先搜索,可以找到从(x,y)至棋盘上所有可达点的最少步数。而问题中要求的是黑马所在的(x1,y1)和白马所在(x2,y2)到达 (1,1) 目标点的最少步数。虽然两条路径的起点不一样,但是它们的终点却是一样的。如果我们将终点(1,1)作为起点,这样只需要一次广度优先搜索便可以得到(x1,y1)和(x2,y2)到达(1,1)的最少步数。

2、数据结构 设queue——队列,存储从(1,1)可达的点(queue[k][1..2])以及到达该点所需要的最少步数(queue[k][3])(0≤k≤192+1)。队列的首指针为head,尾指针为tail。初始时,queue中只有一个元素为(1,1),最少步数为0。 S —记录(1,1)到每点所需要的最少步数。显然,问题的答案是s[x1][y1]和s[x2][y2]。初始时,s[1][1]为0,除此之外的所有元素值设为-1。 dx、dy——移动后的位置增量数组。马有12种不同的扩展方向: 马走“日”: (x-2,y-1)(x-1,y-2)(x-2,y+1)(x-1,y+2)(x+2,y-1)(x+1,y-2)(x+2,y+1)(x+1,y+2) 马走“田”: (x-2,y-2)(x-2,y+2)(x+2,y-2)(x+2,y+2) 我们将i方向上的位置增量存入常量数组dx[i]、dy[i]中(0≤i≤11) int dx[12]={-2,-2,-1,1,2,2,2,2,1,-1,-2,-2}, dy[12]={-1,-2,-2,-2,-2,-1,1,2,2,2,2,1};

3、约束条件 ⑴不能越出界外。由于马的所有可能的落脚点s均在s的范围内,因此一旦马越出界外,就将其s值赋为0,表示“已经扩展过,且(1,1)到达其最少需要0步”。这看上去是荒谬的,但可以简单而有效地避免马再次落入这些界外点。 ⑵该点在以前的扩展中没有到达过。如果曾经到达过,则根据广度优先搜索的原理,先前到达该点所需的步数一定小于当前步数,因此完全没有必要再扩展下去。 由此得出,马的跳后位置(x,y)是否可以入队的约束条件是s[x][y]<0。

代码

#include<iostream>
#include<cstring>
using namespace std;
int ax[12]={-2,-2,-1,1,2,2,2,2,1,-1,-2,-2};
int ay[12]={-1,-2,-2,-2,-2,-1,1,2,2,2,2,1};
int main()
{
    int s[101][101],queue[10000][4]={0},x1,y1,x2,y2;
    memset(s,-1,sizeof(s));
    s[0][0]=1;
    int head=1,tail=1;
    queue[1][1]=1;queue[1][2]=1;queue[1][3]=0;
    cin>>x1>>y1>>x2>>y2;
    while(head<=tail)
    {
        for(int i=0;i<=11;i++)
        {
            int x=queue[head][1]+ax[i];
            int y=queue[head][2]+ay[i];
                if(x>0&&y>0)
                    if(s[x][y]==-1)
                    {
                        s[x][y]=queue[head][3]+1;
                        tail++;
                        queue[tail][1]=x;
                        queue[tail][2]=y;
                        queue[tail][3]=s[x][y];
                    }
                    if(s[x1][y1]>0&&s[x2][y2]>0) 
                    {
                        cout<<s[x1][y1]<<endl<<s[x2][y2];
                        return 0;
                    }
        }
        head++;
    }
    return 0;
}
共 7 篇博客