C - Palindrome URAL - 1297

最新推荐文章于 2019-01-20 14:00:04 发布

原创最新推荐文章于 2019-01-20 14:00:04 发布 · 236 阅读

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针对U.S.Robots遭遇的间谍威胁，前雇员John Pupkin被委任拦截竞争对手Robots Unlimited的隐藏信息。任务关键在于找到文章中由间谍发布、可正反读的最长回文串。采用Manacher算法，John需处理长达1000字符的输入，忽略空格和标点，找出秘密消息。

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C - Palindrome URAL - 1297

The “U.S. Robots” HQ has just received a rather alarming anonymous letter. It states that the agent from the competing «Robots Unlimited» has infiltrated into “U.S. Robotics”. «U.S. Robots» security service would have already started an undercover operation to establish the agent’s identity, but, fortunately, the letter describes communication channel the agent uses. He will publish articles containing stolen data to the “Solaris” almanac. Obviously, he will obfuscate the data, so “Robots Unlimited” will have to use a special descrambler (“Robots Unlimited” part number NPRx8086, specifications are kept secret).
Having read the letter, the “U.S. Robots” president recalled having hired the “Robots Unlimited” ex-employee John Pupkin. President knows he can trust John, because John is still angry at being mistreated by “Robots Unlimited”. Unfortunately, he was fired just before his team has finished work on the NPRx8086 design.
So, the president has assigned the task of agent’s message interception to John. At first, John felt rather embarrassed, because revealing the hidden message isn’t any easier than finding a needle in a haystack. However, after he struggled the problem for a while, he remembered that the design of NPRx8086 was still incomplete. “Robots Unlimited” fired John when he was working on a specific module, the text direction detector. Nobody else could finish that module, so the descrambler will choose the text scanning direction at random. To ensure the correct descrambling of the message by NPRx8086, agent must encode the information in such a way that the resulting secret message reads the same both forwards and backwards.
In addition, it is reasonable to assume that the agent will be sending a very long message, so John has simply to find the longest message satisfying the mentioned property.
Your task is to help John Pupkin by writing a program to find the secret message in the text of a given article. As NPRx8086 ignores white spaces and punctuation marks, John will remove them from the text before feeding it into the program.
Input
The input consists of a single line, which contains a string of Latin alphabet letters (no other characters will appear in the string). String length will not exceed 1000 characters.
Output
The longest substring with mentioned property. If there are several such strings you should output the first of them.
Example
input
Kazak
output
aza

题解：输出原来字符串中的回文串
解题思路：直接用manacher取求回文串

#include<iostream>
#include<string>
using namespace std;
const int inf = 1e4;
string s;
char sn[inf];
int p[inf];
int main()
{	
	while(cin>>s){
		for(int i=1;i<=s.length();i++){sn[i*2-1]='$',sn[i*2]=s[i-1];}
		sn[s.length()*2+1]='$';
		int pos=0,R=0;
		int len=s.length()*2+1;
		for(int i=1;i<=len;i++){
			if(i<R)p[i]=min(p[pos*2-i],R-i);else p[i]=1;
			while(i+p[i]<=len&&i-p[i]>=1&&sn[i+p[i]]==sn[i-p[i]])p[i]++;
			if(i+p[i]>R){
				pos=i;R=i+p[i];
			}
		}
		int ans=0;pos=0;
		for(int i=1;i<=len;i++)if(ans<p[i]){ans=p[i];pos=i;}
		//ans--;int j;
		//if(ans%2){j=pos-ans/2;r=ans/2+1;}
		//else {}
		//cout<<ans-1<<endl;
			//cout<<pos<<"----"<<ans-1<<endl;
		for(int i=pos-p[pos]+1;i<pos+p[pos];i++){
			if(i%2==0)cout<<s[i/2-1];
		}
		cout<<endl;
	}
	return 0;
}