Add solution

Author: Knight

generic/exercise/Cargo.toml

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+[package]
+name = "exercise"
+version = "0.1.0"
+authors = ["Knight <Knight42@mail.ustc.edu.cn>"]
+
+[dependencies]

generic/exercise/README.md

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+README
+=======
+
+`cargo run`

generic/exercise/src/main.rs

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+mod problem1;
+
+fn main() {
+    problem1::demo("Cargo.toml");
+    problem1::demo("");
+}

generic/exercise/src/problem1.rs

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+use std::borrow::Borrow;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+fn parse<I>(lines: I)
+    where I: IntoIterator, I::Item: Borrow<str>
+{
+    for line in lines {
+        println!("{}", line.borrow());
+    }
+}
+
+pub fn demo(path: &str) {
+    if path.is_empty() {
+        println!("==== Parsing long string ====");
+        let content = "some\nlong\ntext";
+        parse(content.lines());
+    } else {
+        println!("==== Parsing text file ====");
+        let f = File::open(path).unwrap();
+        let b = BufReader::new(f);
+        parse(b.lines().map(|l| l.unwrap_or("".to_owned())));
+    }
+}