24 lines
668 B
Java
24 lines
668 B
Java
import java.util.*;
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public class non {
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public static void main(String[] args) {
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Scanner sc = new Scanner(System.in);
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int t = sc.nextInt();
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while (t-- > 0) {
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int n = sc.nextInt();
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long[] x = new long[n];
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long[] y = new long[n];
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for (int i = 0; i < n; i++) {
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x[i] = sc.nextLong();
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y[i] = sc.nextLong();
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}
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long s = 0;
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for (int i = 0; i < n; i++) {
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s += x[i] * y[(i + 1) % n];
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s -= x[(i + 1) % n] * y[i];
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}
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System.out.printf("%.3f\n", Math.abs(s)*0.5);
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}
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}
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}
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