104 lines
2.4 KiB
Rust
104 lines
2.4 KiB
Rust
use std::collections::HashMap;
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type CacheKey = (i32, char);
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struct Cache {
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cache: HashMap<CacheKey, i32>,
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}
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impl Cache {
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const MODULO: i32 = 1000000007;
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fn new() -> Cache {
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let mut cache = HashMap::<CacheKey, i32>::new();
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for c in "aeiou".chars() {
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cache.insert((1, c), 1);
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}
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Cache { cache: cache }
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}
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fn is_precomputed(&self, n: i32) -> bool {
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self.cache.keys().any(|key| key.0 == n)
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}
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fn get(&self, n: i32) -> i32 {
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self.cache
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.keys()
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.filter(|key| key.0 == n)
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.fold(0, |acc, key| {
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// Since the answer may be too large, return it modulo 10^9 + 7.
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(acc + self.cache.get(key).unwrap_or(&0)) % Self::MODULO
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})
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}
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fn precompute(&mut self, n: i32) {
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if self.is_precomputed(n) {
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return;
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}
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if !self.is_precomputed(n - 1) {
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self.precompute(n - 1);
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}
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for (current, continuation) in vec![
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('a', "e"),
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('e', "ai"),
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('i', "aeou"),
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('o', "iu"),
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('u', "a"),
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] {
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self.cache.insert(
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(n, current),
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continuation.chars().fold(0, |acc, vowel| {
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(acc + self.cache.get(&(n - 1, vowel)).unwrap()) % Self::MODULO
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}),
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);
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}
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}
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}
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struct Solution {}
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impl Solution {
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pub fn count_vowel_permutation(n: i32) -> i32 {
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let mut cache = Cache::new();
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cache.precompute(n);
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cache.get(n)
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_example_1() {
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// Input: n = 1
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// Output: 5
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// Explanation: All possible strings are: "a", "e", "i" , "o" and "u".
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assert_eq!(count_vowel_permutation(1), 5);
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}
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#[test]
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fn test_example_2() {
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// Input: n = 2
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// Output: 10
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// Explanation: All possible strings are: All possible strings are: "ae", "ea", "ei", "ia", "ie", "io", "iu", "oi", "ou" and "ua".
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assert_eq!(count_vowel_permutation(2), 10);
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}
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#[test]
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fn test_example_3() {
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// Input: n = 5
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// Output: 68
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assert_eq!(count_vowel_permutation(5), 68);
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}
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#[test]
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fn test_example_4() {
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// Input: n = 3
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// Output: 19
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assert_eq!(count_vowel_permutation(3), 19);
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}
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}
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