PAT甲级 1040 Longest Symmetric String（25 分）贪心算法，最长回文子串

原创于 2018-09-01 22:22:11 发布 · 373 阅读

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本文介绍了一种寻找字符串中最长对称子串的方法，并提供了一个C++实现示例。通过对输入字符串进行逐个字符的比较，判断其是否为对称结构，最终输出最长对称子串的长度。

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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:

解法一:直接使用暴力求解即可，简单~

#include<iostream>
using namespace std;

int l,r,len = -1;

void fun(string str,int i,int j){
	int flag = 0;
	for(int k = i,z=0;k+z <= (i+j)/2;z++){//注意这里需要k=i和z=0 
		if(str[k+z] != str[j-z]){
			flag = 1;
			break;
		}
	}
	if(flag == 0)
	{
		if(len < j-i)
		{
			l = i;
			r = j;
			len = j-i;
		}
	}		
}

int main(){
	string str;
	getline(cin,str);
	
	for(int i=0;i<str.length();i++)
		for(int j=i;j<str.length();j++)
			fun(str,i,j);

	cout<<r-l+1<<endl;
	
	return 0;
}