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a4d674b02e
The trait bounds aren't needed on the struct definition, only the impl block. I think it'd be useful to show the difference here in order to show students how trait bounds for collection types are usually on the impl blocks rather than the type itself.
63 lines
1.7 KiB
Rust
63 lines
1.7 KiB
Rust
// Copyright 2023 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#![allow(unused_variables, dead_code)]
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// ANCHOR: solution
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use std::collections::HashMap;
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use std::hash::Hash;
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/// Counter counts the number of times each value of type T has been seen.
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struct Counter<T> {
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values: HashMap<T, u64>,
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}
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impl<T: Eq + Hash> Counter<T> {
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/// Create a new Counter.
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fn new() -> Self {
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Counter { values: HashMap::new() }
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}
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/// Count an occurrence of the given value.
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fn count(&mut self, value: T) {
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*self.values.entry(value).or_default() += 1;
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}
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/// Return the number of times the given value has been seen.
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fn times_seen(&self, value: T) -> u64 {
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self.values.get(&value).copied().unwrap_or_default()
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}
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}
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// ANCHOR: main
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fn main() {
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let mut ctr = Counter::new();
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ctr.count(13);
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ctr.count(14);
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ctr.count(16);
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ctr.count(14);
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ctr.count(14);
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ctr.count(11);
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for i in 10..20 {
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println!("saw {} values equal to {}", ctr.times_seen(i), i);
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}
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let mut strctr = Counter::new();
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strctr.count("apple");
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strctr.count("orange");
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strctr.count("apple");
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println!("got {} apples", strctr.times_seen("apple"));
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}
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// ANCHOR_END: main
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