赶牛入圈

 

#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> PII;
const int N = 1010; //最多给了500个草的位置，所以最多有1000个数需要离散化
int C, n;
PII points[N]; //存储草的位置
int sum[N][N]; //前缀和数组
vector<int> numbers; //存储所有离散化之后的数
bool check(int len) {
    for (int x1 = 1, x2 = 1; x2 < numbers.size(); x2++) {
        while (numbers[x2] - numbers[x1] + 1 > len) {
            x1++;
        }
        for (int y1 = 1, y2 = 1; y2 < numbers.size(); y2++) {
            while (numbers[y2] - numbers[y1] + 1 > len) {
                y1++;
            }
            if (sum[x2][y2] - sum[x1 - 1][y2] - sum[x2][y1 - 1] + sum[x1 - 1][y1 - 1] >= C) {
                return true;
            }
        }
    }
    return false;
}
int get(int x) {
    int l = 0, r = numbers.size() - 1;
    while (l < r) {
        int mid = (l + r) / 2;
        if (numbers[mid] >= x) {
            r = mid;
        } else {
            l = mid + 1;
        }
    }
    return l;
}
int main() {
    cin >> C >> n;
    numbers.push_back(0);
    for (int i = 0; i < n; i++) {
        int x, y;
        cin >> x >> y;
        numbers.push_back(x);
        numbers.push_back(y);
        points[i] = {x, y};
    }
    sort(numbers.begin(), numbers.end());
    numbers.erase(unique(numbers.begin(), numbers.end()), numbers.end());
    for (int i = 0; i < n; i++) {
        int x = get(points[i].first), y = get(points[i].second);
        sum[x][y]++;
    }
    for (int i = 1; i < numbers.size(); i++) { //计算前缀和
        for (int j = 1; j < numbers.size(); j++) {
            sum[i][j] += sum[i - 1][j] + sum[i][j - 1] - sum[i - 1][j - 1];
        }
    }
    int l = 1, r = 10000; //二分
    while (l < r) {
        int mid = (l + r) / 2;
        if (check(mid)) {
            r = mid;
        } else {
            l = mid + 1;
        }
    }
    cout << l << endl;
    return 0;
}