Node.js) 백준 2166번: 다각형의 면적

https://www.acmicpc.net/problem/2166

2166번: 다각형의 면적

 

const input = require('fs').readFileSync('./dev/stdin').toString().trim().split('\n');
const N = +input.shift();

const points = input.map((v) => v.split(' ').map(Number));

function calc(i, j) {
        const [x1, y1] = points[0];
        const [x2, y2] = points[i];
        const [x3, y3] = points[j];
        return (x1 * y2 + x2 * y3 + x3 * y1 - y1 * x2 - y2 * x3 - y3 * x1) / 2;
}

let answer = 0;
for (let i = 0; i < N - 1; i++) {
        answer += calc(i, i + 1);
}
console.log(Math.abs(Math.round(answer * 10) / 10).toFixed(1));