PAT1040

简单dp，有O(n)做法，这里O(n^2)水过
 1 #include <fstream>
 2 #include <iostream>
 3 #include <vector>
 4 #include <string>
 5 
 6 using namespace std;
 7 
 8 #define OJ
 9 
10 #ifdef OJ
11 #define fin cin
12 #else
13 ifstream fin("in.data");
14 #endif
15 
16 int dp(const string &str){
17     int size = str.size();
18     vector<vector<bool> > f(size, vector<bool>(size, false));
19 
20     for (int i = 0; i < size; i++)
21         f[i][i] = true;
22 
23     int res = 1;
24 
25     for (int len = 2; len <= size; len++){
26         for (int s = 0; s <= size - len; s++){
27             int e = s + len - 1;
28             if (str[s] == str[e] && ((s + 1 > e - 1) || (f[s + 1][e - 1]))){
29                 f[s][e] = true;
30                 if (len > res)
31                     res = len;
32             }
33         }
34     }
35 
36     return res;
37 }
38 
39 int main(){
40     string str;
41     getline(cin, str);
42 
43     cout << dp(str) << endl;
44 
45     return 0;
46 }