[647. Palindromic Substrings] #leetcode

647_0906.java

class Solution {
  // O(n^2) O(n^2)
    public int countSubstrings(String s) {
        int n = s.length();
        
        int[][] dp = new int[n][n];
        int res = 0;
        
        for (int i = n - 1; i >= 0; i--) {
            dp[i][i] = 1;
            res++;
            for (int j = i+1; j < n; j++) {
                if (s.charAt(i) == s.charAt(j) && (i+1 == j || dp[i+1][j-1] == 1)) {
                    dp[i][j] = 1;
                    res++;
                } 
            }
        }
        return res;
    }
}