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# poj 1054（注意审题和理解题意，只考虑超过三个脚印的青蛙，如果存在青蛙脚印，则必须是连续的，即按规律之前和之后都不能有空格）

5小时前 3次浏览
```#include<iostream>
#include<algorithm>
using namespace std;
typedef struct node{
int x,y;
}Point;
Point point[5005];
int r,c,n;
int qcmp(const void*a,const void*b){
Point *p1 = (Point*)a;
Point *p2 = (Point*)b;
if(p1->x>p2->x||(p1->x==p2->x&&p1->y>p2->y))return 1;
if(p1->x==p2->x&&p1->y==p2->y)return 0;
return -1;
}
int cmp(Point p1,Point p2){
if(p1.x<p2.x||(p1.x==p2.x&&p1.y<p2.y))return true;
return false;
}
bool isIn(int x,int y){
if(x<=0||x>r||y<=0||y>c)return false;
return true;
}
bool search(int x,int y){
int mid,l = 0,r = n;
while(l<=r){
mid = (l+r)/2;
if(point[mid].x==x&&point[mid].y==y)return true;
if(point[mid].x<x||(point[mid].x==x&&point[mid].y<y))l = mid+1;
else r = mid-1;
}
return false;
}
int main(){
scanf("%d%d%d",&r,&c,&n);
for(int i=0;i<n;i++){
scanf("%d%d",&point[i].x,&point[i].y);
}
//    sort(point,point+n,cmp);
qsort(point,n,sizeof(Point),qcmp);
int max_num = 0;
for(int i=0;i<n;i++){
for(int j=i+1;j<n;j++){
int x = point[j].x-point[i].x;
int y = point[j].y-point[i].y;
if(isIn(point[i].x-x,point[i].y-y)||
!isIn(point[i].x+max_num*x,point[i].y+max_num*y))continue;
int num = 0;
for(int k=1;isIn(point[j].x+k*x,point[j].y+k*y);k++){
if(search(point[j].x+k*x,point[j].y+k*y))num++;
else{
num = 0;
break;
}
}
max_num = max(num,max_num);
}
}
if(max_num)max_num += 2;
printf("%dn",max_num);
return 0;
} ```