Longest Palindromic Subsequence Problem
Description
LeetCode Problem 516.
Given a string s, find the longest palindromic subsequence’s length in s.
A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.
Example 1:
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Input: s = "bbbab"
Output: 4
Explanation: One possible longest palindromic subsequence is "bbbb".
Example 2:
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Input: s = "cbbd"
Output: 2
Explanation: One possible longest palindromic subsequence is "bb".
Constraints:
- 1 <= s.length <= 1000
- s consists only of lowercase English letters.
Sample C++ Code
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class Solution {
public:
int longestPalindromeSubseq(string s) {
int n = s.size();
vector<vector<int>> dp(n+1,vector<int>(n));
for (int i = 0; i < n; i++)
dp[1][i] = 1;
for (int i = 2; i <= n; i++)
for (int j = 0; j < n-i+1; j++)
dp[i][j] = (s[j]==s[i+j-1]) ? (2 + dp[i-2][j+1]) : max(dp[i-1][j], dp[i-1][j+1]);
return dp[n][0];
}
};