Day46 ＞＞ 647. 回文子串 + 516.最长回文子序列

代码随想录-动态规划Part13

647. 回文子串

class Solution { public int countSubstrings(String s) { boolean[][] dp = new boolean[s.length()][s.length()]; int res = 0; for (int i = s.length() - 1; i >= 0; i--) { for (int j = i; j < s.length(); j++) { if (s.charAt(i) == s.charAt(j) && (j - i <= 1 || dp[i + 1][j - 1])) { res++; dp[i][j] = true; } } } return res; } }

516.最长回文子序列

public class Solution { public int longestPalindromeSubseq(String s) { int len = s.length(); int[][] dp = new int[len + 1][len + 1]; for (int i = len - 1; i >= 0; i--) { // 从后往前遍历 保证情况不漏 dp[i][i] = 1; // 初始化 for (int j = i + 1; j < len; j++) { if (s.charAt(i) == s.charAt(j)) { dp[i][j] = dp[i + 1][j - 1] + 2; } else { dp[i][j] = Math.max(dp[i + 1][j], Math.max(dp[i][j], dp[i][j - 1])); } } } return dp[0][len - 1]; } }