LeetCode每日一题(28. Find the Index of the First Occurrence in a String)

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.

用 Rabin-Karp 算法

impl Solution {pub fn str_str(haystack: String, needle: String) -> i32 {let needle_hash = needle.chars().fold(0, |mut h, c| {h *= 256;h += c as i32;h %= 101;h});let power = (1..needle.len()).fold(1, |mut p, _| {p *= 256;p %= 101;p});let mut haystack_hash = 0;let mut queue = Vec::new();for (i, c) in haystack.chars().enumerate() {if queue.len() == needle.len() {haystack_hash += 101;haystack_hash -= queue.remove(0) as i32 * power % 101;}haystack_hash *= 256;haystack_hash += c as i32;haystack_hash %= 101;queue.push(c);if queue.len() == needle.len() && needle_hash == haystack_hash && haystack[i + 1 - needle.len()..i + 1] == needle[..] {return (i + 1 - needle.len()) as i32;}}-1}
}