原题：ARC076E

洛谷上 UKE，所以到原网交，21 个点只对了 17 个，蒟蒻跪下求大佬帮忙 DEBUG！

源码呈上：

#include <iostream>
#include <vector>
#include <array>
#include <stack>
#include <algorithm>

using std::ios, std::cin, std::cout, std::endl;
using std::vector, std::stack, std::pair, std::array;
using std::sort, std::swap, std::make_pair;

using number = long long;

const int MAXN = 100005;

vector< pair<number, number> > have_it;
vector< pair<number, number> > dot_location;
stack<number> check_stack;
array<bool, MAXN> visited;
number r, c, n;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> r >> c >> n;
    for (int i = 0; i < n; i++) {
        number x1, y1, x2, y2;
        cin >> x1 >> y1 >> x2 >> y2;
        if (x1 != 0 || x1 != r || y1 != 0 || y1 != c) {
            i--;
            n--;
        } else if (x2 != 0 || x2 != r || y2 != 0 || y2 != c) {
            i--;
            n--;
        }
        number loc1 = 0, loc2 = 0;
        if (y1 == 0) {
            loc1 = x1;
        } else if (x1 == r) {
            loc1 = r + y1;
        } else if (y1 == c) {
            loc1 = r * 2 + c - x1;
        } else if (x1 == 0) {
            loc1 = 2 * (r + c) - y1;
        }
        if (y2 == 0) {
            loc2 = y2;
        } else if (x2 == r) {
            loc2 = r + y2;
        } else if (y2 == c) {
            loc2 = r * 2 + c - x2;
        } else if (x2 == 0) {
            loc2 = 2 * (r + c) - y2;
        }
        have_it.push_back(make_pair(loc1, loc2));
    }
    for (int i = 0; i < n; i++) {
        dot_location.push_back(make_pair(have_it[i].first, static_cast<number>(i)));
        dot_location.push_back(make_pair(have_it[i].second, static_cast<number>(i)));
    }
    sort(dot_location.begin(), dot_location.end());
    for (int i = 0; i < 2 * n; i++) {
        pair<number, number> get = dot_location[i];
        if (!visited[get.second]) {
            check_stack.push(get.second);
            visited[get.second] = true;
        } else {
            if (check_stack.top() != get.second) {
                cout << "NO" << endl;
                return 0;
            }
            check_stack.pop();
        }
    }
    cout << "YES" << endl;
    return 0;
}

快快快！