[HDU][4007][Dave]

题目：http://acm.hdu.edu.cn/showproblem.php?pid=4007

给定一些点和一个正方形，求正方形能圈住的最多点数。

参考了P103的黑书。 

#include <stdio.h>
#include <algorithm>

using namespace std;

typedef struct
{
    int x, y;
} point;

bool cmp(point a, point b)
{
    if (a.x == b.x) return a.y < b.y;
    return a.x < b.x;
}

bool cmp2(point a, point b)
{
    if (a.x == b.x) return a.y > b.y;
    return a.x < b.x;
}

point a[1000+5];
point b[10000];

int main(void)
{
    //freopen("D:/a.txt", "r", stdin);
    int n, r;
    while (scanf("%d%d", &n, &r)!=EOF)
    {
        for (int i=0; i<1000; i++)
        {
            a[i].x = 1000000001;
        }
        for (int i=0; i<n; i++)
        {
            scanf("%d%d", &a[i].x, &a[i].y);
        }
        sort(a, a + n, cmp);

        int top=0, max = 0;
        for (int i=0; i<n; i++)
        {
            int max2 = 0;

            top=0;
            int sta = a[i].x, ed = a[i].x + r;
            for (int j=0; j<n; j++)
            {
                if (a[j].x < sta || a[j].x > ed) continue;
                b[top].x = a[j].y;
                b[top].y = 1;
                top++;
                b[top].x = a[j].y + r + 1;
                b[top].y = -1;
                top++;
            }

            sort(b, b+top, cmp2);
            int sum = 0;
            for (int i=0; i<top; i++)
            {
                sum += b[i].y;
                max2 = max2 > sum ? max2 : sum;
            }

            max = max > max2 ? max : max2;
        }
        printf("%d\n", max);
    }
    return 0;
}