day39

回文子串

class Solution {
public:
int countSubstrings(string s) {
int ret = 0;
vector<vector> dp(s.size(), vector(s.size(), 0));
for(int i = s.size() - 1; i >= 0; --i)
{
for(int j = i; j < s.size(); ++j)
{
if(s[i] == s[j])
{
if(j-i <= 1)
{
ret++;
dp[i][j] = true;
}
else if(dp[i+1][j-1])
{
ret++;
dp[i][j] = true;
}
}
}
}
return ret;
}
};

最长回文子序列

class Solution {
public:
int longestPalindromeSubseq(string s) {
vector<vector> dp(s.size(), vector(s.size(), 0));
for(int i = 0; i < s.size(); ++i)
{
dp[i][i] = 1;
}
for(int i = s.size()-2; i >= 0; --i)
{
for(int j = i + 1; j < s.size(); ++j)
{
if(s[i] == s[j])
{
dp[i][j] = dp[i+1][j-1] + 2;
}
else
{
dp[i][j] = max(dp[i+1][j], dp[i][j-1]);
}
}
}
return dp[0][s.size()-1];
}
};