1040 Longest Symmetric String

最长对称子串算法

最新推荐文章于 2021-02-28 11:11:31 发布

原创最新推荐文章于 2021-02-28 11:11:31 发布 · 454 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#pat #string

PAT (Advanced Level) 专栏收录该内容

68 篇文章

订阅专栏

本文介绍了一种用于寻找字符串中最长对称子串的算法实现，并提供了完整的C++代码示例。该算法通过遍历字符串，分别检查以每个字符为中心的奇数长度和偶数长度的对称子串。

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:

#include<iostream>
#include<string>
using namespace std;
int main(){
	for(string str;getline(cin,str);){
		int max_length = 1;
		for(int i = 0; i < str.length();i++){
			int length1 = 1;
			int length2 = 1;
			//判断长度为偶数的情况
			int index_1 = i;
			int index_2 = i+1;
			if(index_1 < 0 || index_2 >= str.length()){
				continue;
			}
			if(str[index_1] == str[index_2]){
				length1 = 2;
				while(1){
					index_1--;
					index_2++;
					if(index_1 < 0  || index_2 >= str.length()){
						break;
					}
					if(str[index_1] == str[index_2]){
						length1+=2;
					}else{
						break;
					}
				}
			}
			//判断长度为奇数的情况
			index_1 = i-1;
			index_2 = i+1;
			if(index_1 < 0 || index_2 >= str.length()){
				continue;
			}
			if(str[index_1] == str[index_2]){
				length2 = 3;
				while(1){
					index_1--;
					index_2++;
					if(index_1 < 0 || index_2 >= str.length()){
						break;
					}
					if(str[index_1] == str[index_2]){
						length2+= 2;
					}else{
						break;
					}
				}
			}
			if(length1 > max_length){
				max_length = length1;
			}
			if(length2 > max_length){
				max_length = length2;
			}
		}
		cout<<max_length<<endl;
	}
	return 0;
}