hdu 题目2034（水题），2036（水，简单计算多边形面积）,2037(水，贪心，会场安排类)

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
using namespace std;
int a[110],c[110],n,mark[110];

int find(int b){
for(int i=0;i<n;i++){
if(a[i]==b) return i;
}
return -1;
}
int main()
{
int j,k,cnt,m,i,b;
while(scanf("%d%d",&n,&m),n||m){

memset(mark,0,sizeof(mark));

for(i=0;i<n;i++)
scanf("%d",&a[i]);

for(i=cnt=0;i<m;i++){
scanf("%d",&b);
k = find(b);
//		cout<<k<<endl;
if(k>=0){
mark[k]=1;
cnt++;
}
}
if(n==cnt)puts("NULL");
else{
for(i=j=0;i<n;i++)
if(!mark[i]) c[j++] = a[i];
sort(c,c+j);
for(i=0;i<j;i++)
printf("%d ",c[i]);
puts("");
}
}
return 0;
}

#include <stdio.h>

struct point{
int x,y;
}p[105];

double cross(point a,point b){
return a.x*b.y - a.y*b.x;
}
int main()
{
int n,i;double sum;
while(scanf("%d",&n),n){
for(i=0;i<n;i++){
scanf("%d%d",&p[i].x,&p[i].y);
}
sum=0;
for(i=0;i<n-1;i++){
sum += cross(p[i],p[i+1]);
}
sum += cross(p[n-1],p[0]);
sum /= 2.0;
printf("%.1lf\n",sum>0?sum:-sum);
}
return 0;
}

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
using namespace std;
struct match{
int s,e;
}a[105];
bool cmp(match i,match j){
return i.e<j.e;
}
int main()
{
int cnt,n,i,last;
while(scanf("%d",&n),n){

for(i=0;i<n;i++)	scanf("%d%d",&a[i].s,&a[i].e);
sort(a,a+n,cmp);
//		for(i=0;i<n;i++)	printf("i=%d,s=%d,e=%d\n",i,a[i].s,a[i].e);
last = a[0].e;
for(cnt=i=1;i<n;i++){
if(a[i].s>=last){	cnt++;	last = a[i].e;	}
}
printf("%d\n",cnt);
}
return 0;
}