1040 Longest Symmetric String

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本文介绍了一种寻找给定字符串中最长对称子串的方法，并提供了一个完整的C++实现示例。通过对输入字符串进行逐个字符检查，该算法确定了最长的对称子串长度。

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1040 Longest Symmetric String （25 分)

Given a string, you are supposed to output the length of the longest symmetric sub-string. For example, given Is PAT&TAP symmetric?, the longest symmetric sub-string is s PAT&TAP s, hence you must output 11.

Input Specification:

Each input file contains one test case which gives a non-empty string of length no more than 1000.

Output Specification:

For each test case, simply print the maximum length in a line.

Sample Input:

Is PAT&TAP symmetric?

Sample Output:

解析：基础的字符串处理。

#include<bits/stdc++.h>
using namespace std;

#define ee exp(1)
#define p acos(-1)
#define mod 1000000007
#define inf 0x3f3f3f3f
#define ll long long
#define ull unsigned long long
#define mem(a,b) memset(a,b,sizeof(a))
int gcd(int a,int b){return b?gcd(b,a%b):a;}

string s;
int symmetric(string str,int i,int j)
{
	int x=i,y=j;
	for(;i<=(x+y)/2;i++)
	{
		if(s[i]!=s[j--])return 0;
	}
	return true;
}
int main()
{
	getline(cin,s);
	
	int maxlen=1;
	for(int i=0; i<s.size(); i++)
	{
		for(int j=i; j<s.size(); j++)
		{
			if(symmetric(s,i,j))maxlen=max(maxlen,j-i+1);
		}
	}
	printf("%d\n",maxlen);
	return 0;
}