PAT Advanced 1040 Longest Symmetric String (25分)
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
解题思路,分奇数,偶数,进行遍历,向两边散开寻找
#include <iostream> #include <algorithm> using namespace std; int main(){ string s;int ans=1; getline(cin,s); for(int i=0;i<s.length();i++){ int j,k; for(j=1;i-j>=0&&i+j<s.length();j++)/** 奇数 */ if(s[i-j]!=s[i+j]) break; if(2*j-1>ans) ans=2*j-1; if(s[i]==s[i+1])/** 偶数 */ for(k=1;i-k>=0&&i+k+1<s.length();k++) if(s[i-k]!=s[i+k+1]) break; if(2*k>ans) ans=2*k; } cout<<ans; return 0; }