feat(geektime_algo): add 34 string kmp_search

Author: Caitlin Gao

rust/34_string/kmp.rs

@@ -0,0 +1,58 @@
+fn kmp_search(primary: &str, pattern: &str) -> Vec<i32> {
+    if primary.is_empty() || pattern.is_empty() || pattern.len() > primary.len() { return vec![0]; }
+
+    let primary_chars: Vec<char> = primary.chars().collect();
+    let pattern_chars: Vec<char> = pattern.chars().collect();
+    let max_match_lengths = get_failure_function(pattern);
+    let mut count = 0;
+    let m = pattern.len();
+    let mut positions = vec![];
+
+    for i in 0..primary.len() {
+        while count > 0 && pattern_chars[count as usize] != primary_chars[i] {
+            count = max_match_lengths[(count-1) as usize];
+        }
+
+        if pattern_chars[count as usize] == primary_chars[i] {
+            count += 1;
+        }
+
+        if count as usize == m {
+            positions.push((i - m + 1) as i32);
+            count = max_match_lengths[(count-1) as usize];
+        }
+    }
+
+    positions
+}
+
+fn get_failure_function(pattern: &str) -> Vec<i32> {
+    let m = pattern.len();
+    let mut max_match_lengths: Vec<i32> = vec![0; m];
+    let mut max_length: i32 = 0;
+    let pattern_chars: Vec<char> = pattern.chars().collect();
+
+    for i in 1..m {
+        while max_length > 0 && pattern_chars[max_length as usize] != pattern_chars[i] {
+            max_length = max_match_lengths[(max_length-1) as usize];
+        }
+
+        if pattern_chars[i] == pattern_chars[max_length as usize] {
+            max_length += 1;
+        }
+
+        max_match_lengths[i] = max_length;
+    }
+
+    max_match_lengths
+}
+
+fn main() {
+    let primary1 = "abbaabbaaba";
+    let pattern1 = "abbaaba";
+    println!("{:?}", kmp_search(primary1, pattern1)); // 4
+
+    let primary = "abc abcdab abcdabcdabde";
+    let pattern = "bcdabd";
+    println!("{:?}", kmp_search(primary, pattern)); // 16
+}