G++和C++ && POJ 1113 Wall

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PS: 次题目虽然叙述点的个数大于等于3但是并不保证凸包是否存在，所以还要判断一下。经常刷题的孩纸可能会遇到用C++ 可用AC的题目用G++ 却 Wrong Answer. 思考过为什么吗？对于double 类型用%lf 输入用%lf输出是window 环境下VC的标准但不是真正的标准，对于double 类型真正的标准是用%lf输入，用%f输出。所以把%.0lf改为%.0f 在G++环境下面就可用轻松AC了。

还有%lld 和 %I64d, 同时也学习一下控制精度的技巧，比如 printf("%d\n", (int)(ans+0.5)). 设置双精度下的毕竟函数等。

#include <iostream>#include <cstdio>#include <algorithm>#include <vector>#include <cstring>#include <cmath>using namespace std;const double eps = 1e-8;const double pi = acos(-1.0);const int maxn  = 1010;struct point {double x, y;point(double x=0, double y=0):x(x),y(y) {}};int sign(double x) {if(fabs(x)<eps) return 0;return x > 0 ? 1 : -1;}point operator - (point A, point B) {return point(A.x-B.x, A.y-B.y);}double Cross(point A, point B) {return A.x*B.y - A.y*B.x;}double mul(point P, point B, point C) {return Cross(B-P, C-P);}double dis2(point A, point B) {return (A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y);}double dis(point A, point B){double t1 = (A.x-B.x)*(A.x-B.x);double t2 = (A.y-B.y)*(A.y-B.y);return sqrt(t1+t2);}int n, l;point p[maxn], q[maxn];point s; // original.bool cmp(point A, point B) {if(sign(mul(s, A, B))>0) return true;else if(sign(mul(s, A, B))==0 && dis2(s,A) < dis2(s, B))return true;else return false;}int convex_hull(point *a, int n, point *b) {for(int i = 1; i < n; i++) {if(sign(a[i].x-a[0].x)<0 || (sign(a[i].x-a[0].x)==0 && sign(a[i].y-a[0].y)<0)) {swap(a[0],a[i]);}}s = a[0];sort(a, a+n, cmp);int newn = 2;b[0]=a[0], b[1]=a[1];for(int i = 2; i < n; i++) {while(newn>1 && sign(mul(b[newn-1], b[newn-2], a[i]))>=0)--newn;b[newn++] = a[i];}return newn;}int main() {scanf("%d%d", &n, &l);for(int i = 0; i < n; i++) {scanf("%lf%lf", &p[i].x, &p[i].y);}int len = convex_hull(p, n, q);if(len < 3) {        printf("0\n");        return 0;    }q[len] = q[0];double ans = 0;for(int i = 0; i < len; i++) {ans += dis(q[i], q[i+1]);}ans += 2*pi*l;    printf("%.0f\n", ans); #ifdef Mprintf("%.0f\n", ans);  // G++ AC，C++ AC。printf("%d\n",(int)(ans+0.5)); G++ AC.printf("%.0lf\n", ans); C++ AC, G++ WA.#endifreturn 0;}

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