[initial] first edition

.gitignore

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+/target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "course_1"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "course_1"
+version = "0.1.0"
+edition = "2024"
+default-run = "main"
+
+[[bin]]
+name = "main"
+path = "src/main.rs"
+
+[[bin]]
+name = "other_binary"
+path = "src/other_binary.rs"
+
+[dependencies]

src/main.rs

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+fn main() {
+    // question 1
+    println!(
+        "Sum of the reciprocal of square roots from 1 to 1,000,000 is {}",
+        (1..=1_000_000)
+            .map(|i| 1.0f64 / (i as f64).sqrt())
+            .sum::<f64>()
+    );
+
+    // question 2
+    let mut input = String::new();
+    std::io::stdin()
+        .read_line(&mut input)
+        .expect("Failed to read line");
+    println!("Counts of characters is {}", input.trim().len());
+
+    // question 3
+    (2..=10000)
+        .filter(|&n| is_perfect(n))
+        .for_each(|n| println!("{} is perfect number.", n));
+}
+
+/// find number's factors first,
+/// and add them to check whether it is a perfect number
+fn is_perfect(number: u64) -> bool {
+    // number == (1..=number / 2).filter(|i| number % i == 0).sum::<u64>()
+    number
+        == 1 + (2..=number.isqrt())
+            .filter(|i| number % i == 0)
+            .map(|i| i + number / i * (i * i != number) as u64)
+            .sum::<u64>()
+}

src/other_binary.rs

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+use std::io;
+
+fn perfect(i: i32) -> bool {
+    let mut sum = 0;
+    for a in 1..i {
+        if i % a == 0 {
+            sum += a;
+        }
+    }
+    sum == i
+}
+
+fn main() {
+    let mut sum: f32 = 0.0;
+    for i in 1..=10000 {
+        sum += 1.0 / f32::sqrt(i as f32);
+    }
+    println!("第一个问题的答案：和为{}", sum);
+
+    println!("请输入一些字符");
+    let mut input = String::new();
+    io::stdin().read_line(&mut input).expect("读取失败");
+    println!("你输入的字符串长度为{}", input.trim().chars().count());
+
+    for j in 1..=10000 {
+        if perfect(j) {
+            println!("{}", j);
+        }
+    }
+}