2017年上海金马五校程序设计竞赛：Find Palindrome_problem e : find palindrome-优快云博客

本文介绍了一种算法，用于从给定字符串中找到最长的回文子串，并提供了详细的实现代码示例。

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Description

Given a string S, which consists of lowercase characters, you need to find the longest palindromic sub-string.

A sub-string of a string S is another string S' that occurs "in" S. For example, "abst" is a sub-string of "abaabsta". A palindrome is a sequence of characters which reads the same backward as forward.

Input

There are several test cases.
Each test case consists of one line with a single string S (1 ≤ |S | ≤ 50).

Output

For each test case, output the length of the longest palindromic sub-string.

Sample Input

sasadasa
bxabx
zhuyuan

Sample Output

7
1
3

#include <bits/stdc++.h>
using namespace std;
int xd(char a[],int w,int i,int j)
{
    int u=0;
    while(j>i)//j即倒数字符要一直大于i即正数字符
    {
        if(a[i]==a[j]&&a[i+1]==a[j-1])//如果相等并且下一对也相等，则数目加2；否则不匹配数目归零
        {
            u=u+2;
        }
        else
        {
            u=0;
        }
        i=i+1;
        j=j-1;
    }
    if(i==j)//如果是回文串是奇数则数目加一，如果不是，则不加
    {
        u=u+1;
    }
    return u;
}
int main()
{
    int n,i,j,q,w,u,v;
    char a[51];
    while(gets(a))
    {
        i=0;
        u=0;
        w=strlen(a);
        j=w-1;
        for(i=0;i<w;i++)//循环比较开始字符和倒数字符
            for(j=w-1;j>=i;j--)
        {
            if(a[i]==a[j])//如果相等则进去函数
            {
                v=xd(a,w,i,j);
                if(v>u)
                    u=v;
            }
        }
        cout<<u<<endl;
    }
    return 0;
}