Count prefix and suffix pairs i

Array String Trie Rolling Hash String Matching Hash Function

77.8% acceptance

Feb 25, 2026

602

You are given a 0-indexed string array words. Let's define a boolean function isPrefixAndSuffix that takes two strings, str1 and str2: isPrefixAndSuffix(str1, str2) returns true if str1 is both a prefix and a suffix of str2, and false otherwise. Return an integer denoting the number of index pairs (i, j) such that i < j, and isPrefixAndSuffix(words[i], words[j]) is true.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn count_prefix_suffix_pairs(words: Vec<String>) -> i32 {
    let n = words.len();
    let mut ans = 0;
    for i in 0..n {
      for j in (i+1)..n {
        let s = &words[i];
        let t = &words[j];
        if t.starts_with(s.as_str()) && t.ends_with(s.as_str()) { ans += 1; }
      }
    }
    ans
  }
}