PAT1040. Longest Symmetric String

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思路：最长回文子串，O（n^2）的算法。本次算法编程知道了一些语法上的问题例如：用string时 如用cin>>输入那么就会产生遇到空格断开，并且gets()不能读取string。

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <string>
 5 using namespace std;
 6 #define MAX 1010
 7 int dp[MAX][MAX];
 8 int ans;
 9 int main(int argc, char *argv[])
10 {
11     char str[MAX];
12     //cin>>string 也是读到空格结束 get不能读string
13     gets(str);             //在cstdio中
14     int len=strlen(str);
15     memset(dp,0,sizeof(dp));
16     ans=1;
17     //对dp进行初始化
18     for(int i=0;i<len;i++)
19     {
20         dp[i][i]=1;
21         if(i<len-1)
22         {
23             if(str[i]==str[i+1])
24             {
25                 dp[i][i+1]=1;
26                  ans=2;
27             }
28         }
29
30     }
31     for(int l=3;l<=len;l++)
32     {
33         for(int i=0;i+l-1<len;i++)
34         {
35             int j=i+l-1;
36             if(str[i]==str[j])
37             {
38                 dp[i][j]=dp[i+1][j-1];
39                 ans=l;// 答案错误 如何dp[i+1][j-1]=0的时候那么不成立
40             }
41             else
42                 dp[i][j]=0;
43         }
44     }
45     cout<<ans<<endl;
46     return 0;
47 }