题解 | #计算一元二次方程#

use std::io::{self, *};

fn main() {
    let stdin = io::stdin();
    for line in stdin.lock().lines() {
        let ll = line.unwrap();
        let numbers: Vec<&str> = ll.split(" ").collect();
        if numbers.len() != 3 {
            println!("请输入二元一次方程组的三个参数！");
            continue;
        }
        let a = numbers[0].trim().parse::<f64>().unwrap_or(0.0);
        let b = numbers[1].trim().parse::<f64>().unwrap_or(0.0);
        let c = numbers[2].trim().parse::<f64>().unwrap_or(0.0);
        cal_quadratic_equation(a, b, c);
    }
}

/// # 功能
/// 计算一元二次方程组并打印结果
/// # 参数
/// * `a` - 平方项系数
/// * `b` - 一次方项系数
/// * `c` - 常数项
/// # 示例
/// 解二元一次方程 2x^2 + 7x + 1 = 0，
/// 预期结果为`x1=-3.35;x2=-0.15`
/// ```
/// cal_quadratic_equation(2.0, 7.0, 1.0);
/// ```
/// # 备注
/// * 打印精度为小数点后两位
/// * 当方程没有实数解时会打印虚数解（实部+虚部）
fn cal_quadratic_equation(a: f64, b: f64, c: f64) {
    let delta: f64 = b * b - 4.0 * a * c; //判别式
    if a == 0.0 {
        println!("Not quadratic equation");
    } else {
        if delta == 0.0 {
            println!("x1=x2={:.2}", -b / (2.0 * a));
        } else if delta > 0.0 {
            println!(
                "x1={:.2};x2={:.2}",
                (-b - delta.sqrt()) / (2.0 * a),
                (-b + delta.sqrt()) / (2.0 * a)
            );
        } else if delta < 0.0 {
            let real_quantity = -b / (2.0 * a); //实部
            let imaginary_quantity = (-delta).sqrt() / (2.0 * a); //虚部
            println!(
                "x1={:.2}-{:.2}i;x2={:.2}+{:.2}i",
                real_quantity, imaginary_quantity, real_quantity, imaginary_quantity
            );
        }
    }
}