UVA - 1382 Distant Galaxy

题目大意：给出 n 个点，问说一个平行与 x 轴和 y 轴的矩形，最多能有多少个点落在边上。

解题思路：首先先将 y 轴相同的放在一起，然后枚举左右边界，考虑上下边界，维护最大值

#include <cstdio>
#include <algorithm>
using namespace std;

struct Point {
    int x;
    int y;
    bool operator < (const Point& a) const {
        return  x < a.x;
    }
};

const int maxn = 100 + 10;
Point P[maxn];
int y[maxn], on[maxn], on2[maxn], left[maxn];

int solve(int N) {
    sort(P, P + N);
    sort(y, y + N);
    int m = unique(y, y + N) - y;
    if (m <= 2) return N;

    int ans = 0;
    for (int a = 0; a < m; a++)
        for (int b = a + 1; b < m; b++) {
            int ymin = y[a], ymax = y[b];

            int k = 0;
            for (int i = 0; i < N; i++) {
                if (i == 0 || P[i].x != P[i-1].x) {
                    k++;
                    on[k] = on2[k] = 0;
                    left[k] = left[k-1] + on2[k-1] - on[k-1];
                }
                if (P[i].y > ymin && P[i].y < ymax) on[k]++;
                if (P[i].y >= ymin && P[i].y <= ymax) on2[k]++;
            }
            if (k <= 2) return N;

            int M = 0;
            for (int j = 1; j <= k; j++) {
                ans = max(ans, left[j] + on2[j] + M);
                M = max(M, on[j] - left[j]);
            }
        }
    return ans;
}

int main() {
    int N, kase = 0;
    while (scanf("%d", &N), N) {
        for (int i = 0; i < N; i++) {
            scanf("%d%d", &P[i].x, &P[i].y);
            y[i] = P[i].y;
        }
        printf("Case %d: %d\n", ++kase, solve(N));
    }
    return 0;
}

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