Find the index of the first occurrence in a string

Two Pointers String String Matching

46.3% acceptance

Jan 12, 2026

7515

571

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn str_str(haystack: String, needle: String) -> i32 {
    if needle.is_empty() {
      return 0;
    }
    
    let haystack_bytes = haystack.as_bytes();
    let needle_bytes = needle.as_bytes();
    let haystack_len = haystack_bytes.len();
    let needle_len = needle_bytes.len();
    
    if needle_len > haystack_len {
      return -1;
    }
    
    for i in 0..=(haystack_len - needle_len) {
      let mut found = true;
      for j in 0..needle_len {
        if haystack_bytes[i + j] != needle_bytes[j] {
          found = false;
          break;
        }
      }
      if found {
        return i as i32;
      }
    }
    
    -1
  }
}