Add boyer moore search (TheAlgorithms#389)

Author: merelymyself

README.md

@@ -114,6 +114,7 @@ These are for demonstration purposes only.
 ## [Strings](./src/string)
 
 - [x] [Aho-Corasick Algorithm](./src/string/aho_corasick.rs)
+- [x] [Boyer-Moore String Search Algorithm](./src/string/boyer_moore_search.rs)
 - [x] [Burrows-Wheeler transform](./src/string/burrows_wheeler_transform.rs)
 - [x] [Knuth Morris Pratt](./src/string/knuth_morris_pratt.rs)
 - [x] [Manacher](./src/string/manacher.rs)

src/string/boyer_moore_search.rs

@@ -0,0 +1,60 @@
+// In computer science, the Boyer–Moore string-search algorithm is an efficient string-searching algorithm,
+// that is the standard benchmark for practical string-search literature. Source: https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_string-search_algorithm
+
+use std::collections::HashMap;
+
+pub fn boyer_moore_search(text: &str, pattern: &str) -> Vec<usize> {
+    let mut positions = Vec::new();
+    let n = text.len() as i32;
+    let m = pattern.len() as i32;
+    let pattern: Vec<char> = pattern.chars().collect();
+    let text: Vec<char> = text.chars().collect();
+    if n == 0 || m == 0 {
+        return positions;
+    }
+    let mut collection = HashMap::new();
+    for (i, c) in pattern.iter().enumerate() {
+        collection.insert(c, i as i32);
+    }
+    let mut shift: i32 = 0;
+    while shift <= (n - m) as i32 {
+        let mut j = (m - 1) as i32;
+        while j >= 0 && pattern[j as usize] == text[(shift + j) as usize] {
+            j -= 1;
+        }
+        if j < 0 {
+            positions.push(shift as usize);
+            let add_to_shift = {
+                if (shift + m) < n {
+                    let c = text[(shift + m) as usize];
+                    let index = collection.get(&c).unwrap_or(&-1);
+                    m - index
+                } else {
+                    1
+                }
+            };
+            shift += add_to_shift;
+        } else {
+            let c = text[(shift + j) as usize];
+            let index = collection.get(&c).unwrap_or(&-1);
+            let add_to_shift = std::cmp::max(1, j - index);
+            shift += add_to_shift;
+        }
+    }
+    positions
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_boyer_moore_search() {
+        let a = boyer_moore_search("AABCAB12AFAABCABFFEGABCAB", "ABCAB");
+        assert_eq!(a, [1, 11, 20]);
+        let a = boyer_moore_search("AABCAB12AFAABCABFFEGABCAB", "FFF");
+        assert_eq!(a, []);
+        let a = boyer_moore_search("AABCAB12AFAABCABFFEGABCAB", "CAB");
+        assert_eq!(a, [3, 13, 22]);
+    }
+}

src/string/mod.rs

@@ -1,4 +1,5 @@
 mod aho_corasick;
+mod boyer_moore_search;
 mod burrows_wheeler_transform;
 mod hamming_distance;
 mod jaro_winkler_distance;
@@ -12,6 +13,7 @@ mod suffix_tree;
 mod z_algorithm;
 
 pub use self::aho_corasick::AhoCorasick;
+pub use self::boyer_moore_search::boyer_moore_search;
 pub use self::burrows_wheeler_transform::{
     burrows_wheeler_transform, inv_burrows_wheeler_transform,
 };