PAT Advanced 1040 Longest Symmetric String

1040 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

解題思路

• 中心擴展

  枚舉字符串中每一個位置，以枚舉的每一個位置作爲中心，向兩邊擴展找到最大長度，需要分兩種情況，存在字符串的長度爲奇數或者偶數

• 動態規劃

解題代碼

• 解法一：

  #include <iostream>
  #include <cstdio>
  using namespace std;
  string s;
  int len;
  void getlen(int l, int r){
      while(l >= 0 && r < s.size() && s[l--] == s[r ++])
      len = max(r - l - 1, len);
  }
  int main(){
     getline(cin, s);
     for (int i = 0; i < s.size(); i++)
          getlen(i, i), getlen(i, i + 1);
     printf("%d", len);
     return 0;
  }