2523883_ac_0ms_156k.cpp

北大大牛代码 1240道题的原代码 超级权威

#include <stdio.h>
#include <algorithm>
#include <math.h>
using namespace std;
# define MAX 1001

struct node
{
	int x, y;
}Q[MAX];

int n, L, low;
int lowx, lowy;
int p, s[MAX];

bool cmp(struct node a,struct node b)
{
	if(a.x==lowx&&a.y==lowy)
		return 1;
	if(b.x==lowx&&b.y==lowy)
		return 0;
	if((a.x-lowx)*(b.y-lowy)==(b.x-lowx)*(a.y-lowy))
		return (a.x-lowx)*(a.x-lowx)+(a.y-lowy)*(a.y-lowy)<(b.x-lowx)*(b.x-lowx)+(b.y-lowy)*(b.y-lowy);
	return (a.x-lowx)*(b.y-lowy)-(b.x-lowx)*(a.y-lowy) > 0;
}

void GRAHAM_SCAN()
{
	int i;

	s[0] = 0;
	i = 1;while(i<n-1&&(Q[i].x-lowx)*(Q[i+1].y-lowy)==(Q[i+1].x-lowx)*(Q[i].y-lowy))
		i++;
	s[1] = i++;s[2] = i++;
	p = 2;
	while(i < n)
	{		
		while((Q[s[p-1]].x-Q[s[p]].x)*(Q[i].y-Q[s[p]].y)>=(Q[i].x-Q[s[p]].x)*(Q[s[p-1]].y-Q[s[p]].y))
			p--;
		s[++p] = i;
		i++;
	}
}

int main()
{
	int i;
	double ans;

	scanf("%d",&n);
	for(i = 0; i < n; i++)
	{
		fscanf(stdin,"%d%d",&Q[i].x,&Q[i].y);
		if(i)
		{
			if(Q[i].y < Q[low].y||(Q[i].y == Q[low].y&&Q[i].x<Q[low].x))
				low = i;
		}
	}
	lowx = Q[low].x; lowy = Q[low].y;
	sort(Q,Q+n,cmp);
	ans = 0;
	GRAHAM_SCAN();
	for(i = 0; i <= p; i++)
		ans += Q[s[i]].x*Q[s[(i+1)%(p+1)]].y-Q[s[i]].y*Q[s[(i+1)%(p+1)]].x;
	ans /= 2;
	if(ans<0)
		ans *= -1;
	printf("%.0lf\n",floor(ans/50));
	return 1;
}