28. Find the Index of the First Occurrence in a String

Problem Statement

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.

Example 1:

Input: haystack = "sadbutsad", needle = "sad"
Output: 0
Explanation: "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.

Example 2:

Input: haystack = "leetcode", needle = "leeto"
Output: -1
Explanation: "leeto" did not occur in "leetcode", so we return -1.

Constraints:

1 <= haystack.length, needle.length <= 10⁴
haystack and needle consist of only lowercase English characters.

Solution:

Rust

impl Solution {
    pub fn str_str(haystack: String, needle: String) -> i32 {
        let (m, n) = (haystack.len(), needle.len());

        if m < n {
            return -1;
        }

        // iterate over the haystack from 0 to m - n
        // because the needle can't be longer than the haystack
        for i in 0..=m - n {
            if haystack[i..i + n] == needle {
                return i as i32;
            }
        }

        -1
    }
}

28. Find the Index of the First Occurrence in a String #

Problem Statement #

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28. Find the Index of the First Occurrence in a String

Problem Statement

Solution:

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