一 最长回文子串
1.1 描述
给定一个字符串str,返回这个字符串的最长回文子序列长度
比如 : str = “a12b3c43def2ghi1kpm”
最长回文子序列是“1234321”或者“123c321”,返回长度7
1.2 分析
1.2.1 先将原传逆序,求原串和反转后的串的最长公共子序列就是原串的最长回文子序列
1.2 反转求最长公共子序列 代码
public static int longestPalindromeSubseq1(String s) {
if (s == null || s.length() == 0) {
return 0;
}
if (s.length() == 1) {
return 1;
}
char[] str = s.toCharArray();
char[] reverse = reverse(str);
return longestCommonSubsequence(str, reverse);
}
public static int longestCommonSubsequence(char[] str1, char[] str2) {
int N = str1.length;
int M = str2.length;
int[][] dp = new int[N][M];
dp[0][0] = str1[0] == str2[0] ? 1 : 0;
for (int i = 1; i < N; i++) {
dp[i][0] = str1[i] == str2[0] ? 1 : dp[i - 1][0];
}
for (int j = 1; j < M; j++) {
dp[0][j] = str1[0] == str2[j] ? 1 : dp[0][j - 1];
}
for (int i = 1; i < N; i++) {
for (int j = 1; j < M; j++) {
dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
if (str1[i] == str2[j]) {
dp[i][j] = Math.max(dp[i][j], dp[i - 1][j - 1] + 1);
}
}
}
return dp[N - 1][M - 1];
}