g0601_0700.s0647_palindromic_substrings.Solution.dart Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

There is a newer version: 1.8

// #Medium #String #Dynamic_Programming #Big_O_Time_O(n^2)_Space_O(n)
// #2024_10_12_Time_313_ms_(90.00%)_Space_148.2_MB_(70.00%)

class Solution {
  void expand(List a, int l, int r, List res) {
    while (l >= 0 && r < a.length) {
      if (a[l] != a[r]) {
        return;
      } else {
        res[0]++;
        l--;
        r++;
      }
    }
  }

  int countSubstrings(String s) {
    List a = s.split(''); // Dart's equivalent of `toCharArray()`
    List res = [0]; // Using a list to mimic the behavior of an int array
    for (int i = 0; i < a.length; i++) {
      expand(a, i, i, res);      // Odd length palindrome
      expand(a, i, i + 1, res);  // Even length palindrome
    }
    return res[0];
  }
}