java 516.最长的回文子序列（＃1）.java

Posted 2021-05-08

class Solution {
    public int longestPalindromeSubseq(String s) {
        if (s == null || s.length() < 1) return 0;
        int len = s.length();
        int[][] dp = new int[len][len];
        for (int i = len - 1; i >= 0 ;i--) {
            dp[i][i] = 1;
            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], dp[i][j - 1]);
                }
            }
        }
        return dp[0][len - 1];
    }
}

class Solution {
    public int longestPalindromeSubseq(String s) {
        if (s == null || s.length() < 1) return 0;
        int len = s.length();
        int[][] dp = new int[len][len];
        for (int i = len - 1; i >= 0 ;i--) {
            for (int j = i; j < len; j++) {
                if (s.charAt(i) == s.charAt(j)) {
                    if ( j - i >= 2) {
                        dp[i][j] = dp[i + 1][ j - 1] + 2;
                    } else {
                        dp[i][j] = j - i + 1;
                    }
                } else {
                    if (j - i >= 2) {
                        dp[i][j] = Math.max(dp[i + 1][j], dp[i][j - 1]);
                    } else {
                        dp[i][j] = 1;
                    }
                    
                }
            }
        }
        return dp[0][len - 1];
    }
}