题目1： 647. 回文子串
代码：
class Solution {
public:
int countSubstrings(string s) {
int n = s.length();
vector<vector<bool>> dp(n, vector<bool>(n));
int total = 0;
for(int i = 0; i < n; i++) {
dp[i][i] = true;
total++;
}
for(int len = 2; len <= n; len++) {
for(int i = 0; i + len <= n; i++) {
int j = i + len - 1;
if(s[i] != s[j]) {
continue;
}
if(len > 2 && !dp[i + 1][j - 1]){
continue;
}
dp[i][j] = true;
++total;
}
}
return total;
}
};
题目2： 516. 最长回文子序列
代码：
class Solution {
public:
int longestPalindromeSubseq(string s) {
int n = s.length();
vector<vector<int>> dp(n, vector<int>(n));
for(int i = 0; i < n; i++) dp[i][i] = 1;
for(int i = n - 1; i >= 0; i--) {
for(int j = i + 1; j < n; j++) {
if(s[i] == s[j]) dp[i][j] = dp[i + 1][j - 1] + 2;
else dp[i][j] = max(dp[i][j - 1], dp[i + 1][j]);
}
}
return dp[0][n - 1];
}
};
