Manacher (#39)

* add manacher

* fix cargo doc

Author: cameroncuster

Cargo.toml

@@ -77,3 +77,7 @@ path = "examples/numbers/primes_factorize.rs"
 [[example]]
 name = "primes_is_prime"
 path = "examples/numbers/primes_is_prime.rs"
+
+[[example]]
+name = "manacher"
+path = "examples/strings/manacher.rs"

examples/strings/manacher.rs

@@ -0,0 +1,24 @@
+// verification-helper: PROBLEM https://judge.yosupo.jp/problem/enumerate_palindromes
+
+use proconio::input;
+use programming_team_code_rust::strings::manacher::manacher;
+
+fn main() {
+    input! {
+        s: String
+    }
+
+    let man = manacher(&s.chars().collect::<Vec<_>>())
+        .iter()
+        .enumerate()
+        .map(|(i, &x)| i - 2 * x + 1)
+        .collect::<Vec<_>>();
+
+    println!(
+        "{}",
+        man.iter()
+            .map(|&x| x.to_string())
+            .collect::<Vec<_>>()
+            .join(" ")
+    );
+}

src/lib.rs

@@ -2,3 +2,4 @@
 pub mod data_structures;
 pub mod graphs;
 pub mod numbers;
+pub mod strings;

src/strings/manacher.rs

@@ -0,0 +1,44 @@
+//! # Manacher's algorithm
+
+/// See <https://codeforces.com/blog/entry/12143#comment-324162>
+///
+/// subarray [le, ri] has "center" i = le + ri
+///
+/// center 0 2 4 6 8
+/// string b a a b a
+/// center  1 3 5 7
+///
+/// man = {0, 1, 1, 0, 2, 3, 2, 4, 4}
+///
+/// # Example
+/// ```
+/// use programming_team_code_rust::strings::manacher::manacher;
+///
+/// assert_eq!(manacher(&"baaba".chars().collect::<Vec<_>>()), vec![0, 1, 1, 0, 2, 3, 2, 4, 4]);
+/// ```
+///
+/// # Complexity (n = s.len())
+/// - Time: O(n)
+/// - Space: O(n)
+pub fn manacher<T: std::cmp::PartialEq>(s: &[T]) -> Vec<usize> {
+    if s.is_empty() {
+        return vec![];
+    }
+    let n = s.len();
+    let mut p = 0;
+    let mut man = vec![0; 2 * n - 1];
+    for i in 0..2 * n - 1 {
+        let mut ri = if i <= 2 * (p - man[p]) {
+            p - man[p].max(man[2 * p - i])
+        } else {
+            i / 2
+        };
+        man[i] = i - ri;
+        while man[i] > 0 && ri + 1 < n && s[man[i] - 1] == s[ri + 1] {
+            man[i] -= 1;
+            ri += 1;
+            p = i;
+        }
+    }
+    man
+}

src/strings/mod.rs

@@ -0,0 +1,2 @@
+//! # String Algorithms
+pub mod manacher;