Palindromic substrings

Two Pointers String Dynamic Programming

72.6% acceptance

Feb 20, 2026

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Given a string s, return the number of palindromic substrings in it.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn count_substrings(s: String) -> i32 {
    let s = s.as_bytes();
    let n = s.len();
    let mut count = 0;
    for center in 0..2 * n - 1 {
      let mut left = center / 2;
      let mut right = left + center % 2;
      loop {
        if s[left] == s[right] {
          count += 1;
          if left == 0 || right == n - 1 { break; }
          left -= 1;
          right += 1;
        } else {
          break;
        }
      }
    }
    count
  }
}