【PAT】1040. Longest Symmetric String (25)

最新推荐文章于 2019-08-29 09:01:22 发布

realxuejin

最新推荐文章于 2019-08-29 09:01:22 发布

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分类专栏： PAT 文章标签： PAT

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本文介绍了一种求解给定字符串中最长回文子串的算法实现，通过在原字符串中插入特殊字符并以此为中心向两边扩散的方式，寻找最长回文子串，并给出具体示例。

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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:

分析：插入特殊字符。然后以每个字符为中心，两边扩散开来查找。

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int main(){
	string str;
	getline(cin,str);
	vector<int> vec;
	int i,j;
	for(i=0; i<str.size(); i++){
		vec.push_back(-1);
		vec.push_back(str[i]);		
	}
	vec.push_back(-1);
	int left, right, step, max;
	step = 0;
	max = 0;
	for(i=1; i<vec.size(); i++){
		step = 0;
		for(left=i-1,right=i+1; left>=0&&right<vec.size(); --left,++right){
			if(vec[left] != vec[right]){
				break;
			}
			step += 2;		 			
		}		
		if(step > max){
			max = step;
		}
	}
	cout<<max/2<<endl;	
	return 0;
}