1040. Longest Symmetric String (25)

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:
11

方法1：动态规划法#include<cstdio>#include<cstring>const int maxn=1010;char a[maxn];int dp[maxn][maxn];//dp[i][j]等于1表示i到j是回文，等于0表示i到j不是回文int main(){    gets(a);    memset(dp,0,sizeof(dp));    int len=strlen(a),ans=1;    for(int i=0;i<len;i++){        dp[i][i]=1;        if(i<len-1&&a[i]==a[i+1]){            dp[i][i+1]=1;            ans=2;        }    }    for(int L=3;L<=len;L++){        for(int i=0;i+L-1<len;i++){            int j=i+L-1;            if(a[i]==a[j]&&dp[i+1][j-1]==1){                dp[i][j]=1;                ans=L;            }        }    }    printf("%d\n",ans);    return 0;}

方法2：暴力法，最后一个测试点错误，不知错哪里#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int maxn=1010;char a[maxn];int main(){    gets(a);    int len=strlen(a),ans=1;    for(int i=0;i<len;i++){        int j,l=i,r;        for(j=len-1;j>i;j--){            if(a[j]==a[i]){                r=j;                break;            }         }        if(j>i){            while(l<r){                if(a[l]!=a[r]) break;                l++,r--;            }            if(l>=r){                ans=max(ans,j-i+1);            }        }    }    printf("%d\n",ans);    return 0;}