手撕代码：求字符串最长回文子序列

 1 int longestSubSeq(string ss)
 2 {
 3     int n=(int)ss.size();
 4     if(n==0)
 5     {
 6         return 0;
 7     }
 8     //申请辅助内存
 9     int **f=new int* [n];
10     for(int k=0;k<n;++k)
11     {
12         f[k]=new int[n];
13     }
14     //初始化
15     for(int i=0;i<n;++i)
16     {
17         f[i][i]=1;
18         if(i<n-1)
19         {
20             if(ss[i]==ss[i+1])
21             {
22                 f[i][i+1]=2;
23             }
24         }
25     }
26     //计算顺序
27     int len;
28     int Max=1;
29     for(len=3;len<=n;++len)
30         for(int i=0;i<=n-len;++i)
31         {
32             int j=i+len-1;
33             f[i][j]=max(f[i+1][j],f[i][j-1]);
34             if(ss[i]==ss[j])
35             {
36                 f[i][j]=max(f[i][j],f[i+1][j-1]+2);
37                 if(f[i][j]>Max)
38                 {
39                     Max=f[i][j];
40                 }
41             }
42         }
43     //释放内存
44     for (int l = 0; l <n; ++l) {
45         delete [] f[l];
46     }
47     delete []f;
48     return Max;
49 }