题解 | 计算三角形的周长和面积

我们余弦定理怎么你了？🥰

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        if (in.hasNextDouble()) {
            double triangleA = in.nextInt();
            double triangleB = in.nextInt();
            double triangleC = in.nextInt();
            if (
                ((triangleA + triangleB) <= triangleC) ||
                ((triangleA + triangleC) <= triangleB) ||
                ((triangleB + triangleC) <= triangleA)
            ) throw new IllegalArgumentException("Illegal triangle!");

            double totalLength = triangleA + triangleB + triangleC;
            double cosAvalue = (Math.pow(triangleB, 2) + Math.pow(triangleC, 2) - Math.pow(triangleA, 2)) / (2 * triangleB * triangleC);
            double sinAvalue = Math.sqrt(1 - Math.pow(cosAvalue, 2));
            double area = 0.5 * sinAvalue * triangleB * triangleC;
            System.out.println(String.format("circumference=%.2f area=%.2f", totalLength, area));
        }
    }
}