以HDU2108為例，去AC吧。//點逆序輸入 import java.util.Scanner; //1s public class HDU2108 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);while(true) {int x,y;int n = sc.nextInt();if(0==n) {break;}Point[] p = new Point[n];for(int i=0; i<n; i++) {p[i] = new Point();}for(int i=0; i<n; i++) {x = sc.nextInt();y = sc.nextInt();p[i] = new Point(x,y);}//凸多邊形boolean tag = true;int j,k,t;for(int i=0; i<n; i++) {//k,t直接對n求余就行了j = i;k = i+1;t = i+2;//以三角形為例看看if(k==n) {k = 0;}if(t==n+1) {t = 1;}if(t==n) {t = 0;}//注意是后面減去前面的Point p1 = new Point(p[k].x - p[j].x,p[k].y - p[j].y);Point p2 = new Point(p[t].x - p[k].x,p[t].y - p[k].y);//叉積int ans = p1.x*p2.y - p1.y*p2.x;if(ans<0) {tag = false;break;}}if(tag) {System.out.println("convex");}else {System.out.println("concave");}}} } class Point {int x;int y;public Point() {this.x = 0;this.y = 0;}public Point(int x, int y) {this.x = x;this.y = y;} }

轉載于:https://www.cnblogs.com/hxsyl/p/3250152.html

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