05 August 2008
最长回文子序列，跟第5题类似
dp[i][j]: the longest palindromic subsequence’s length of substring(i, j)
状态转移方程: dp[i][j] = dp[i+1][j-1] + 2 if s.charAt(i) == s.charAt(j)
otherwise, dp[i][j] = Math.max(dp[i+1][j], dp[i][j-1])
初始化: dp[0][0] = 1
https://leetcode.com/problems/longest-palindromic-subsequence/discuss/99101/Straight-forward-Java-DP-solution 同时还有自顶向下的例子
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class Solution {
public int longestPalindromeSubseq(String s) {
if (s.isEmpty()) {
return 0;
}
int[][] dp = new int[s.length()][s.length()];
for (int i = s.length() - 1; i >= 0; i--) {
dp[i][i] = 1;
for (int j = i + 1; j < s.length(); 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], dp[i][j - 1]);
}
}
}
return dp[0][s.length() - 1];
}
}