Implement the Knuth-Morris-Pratt algorithmw

rust/find-the-index-of-the-first-occurrence-in-a-string/Cargo.toml

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+[package]
+name = "find-the-index-of-the-first-occurrence-in-a-string"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

rust/find-the-index-of-the-first-occurrence-in-a-string/src/main.rs

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+//! Find the Index of the First Occurrence in a String
+//!
+//! Use the Knuth-Morris-Pratt algorithm
+//!
+//! $\mathcal{O}(|P| + |T|)$ time complexity
+//! where $P$ is the pattern and $T$ is the text searched
+//!
+
+struct Solution;
+
+impl Solution {
+
+    pub fn kmp_search(prefix_table: &Vec<usize>,
+                    pattern: &String,
+                    text: &String) -> i32 {
+        let mut i: usize = 0;
+        let mut j: usize = 0;
+        while i < text.len() {
+            if text.chars().nth(i) == pattern.chars().nth(j) {
+                i += 1;
+                j += 1;
+                if j == pattern.len() {
+                    return i as i32 - j as i32;
+                }
+            } else {
+                if j != 0 {
+                    j = prefix_table[j - 1];
+                } else {
+                    i += 1;
+                }
+            }
+        }
+        return -1;
+    }
+
+    pub fn kmp_prefix(pattern: &String) -> Vec<usize> {
+        let mut table: Vec<usize> = vec![0; pattern.len()];
+
+        table[0] = 0;
+        let mut i = 1;
+        let mut len = 0;
+        while i < pattern.len() {
+            if pattern.chars().nth(i) == pattern.chars().nth(len) {
+                len += 1;
+                table[i] = len;
+                i += 1;
+            } else {
+                if len != 0 {
+                    len = table[len - 1];
+                } else {
+                    table[i] = 0;
+                    i += 1;
+                }
+            }
+        }
+        table
+    }
+
+    pub fn str_str(haystack: String, needle: String) -> i32 {
+        let prefix = Self::kmp_prefix(&needle);
+        Self::kmp_search(&prefix, &needle, &haystack)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::*;
+
+    #[test]
+    fn test_1() {
+        let haystack = "sadbutsad".to_string();
+        let needle = "sad".to_string();
+        let position = Solution::str_str(haystack, needle);
+        assert_eq!(position, 0);
+    }
+
+    #[test]
+    fn test_2() {
+        let haystack = "leetcode".to_string();
+        let needle = "leeto".to_string();
+        let position = Solution::str_str(haystack, needle);
+        assert_eq!(position, -1);
+    }
+}
+
+fn main() {
+    println!("Hello, world!");
+}