範例程式碼 uva1657

//uva1657
#include <iostream>
#include <map>
#include <vector>
#include <unordered_map>


using namespace std;

int main() {
    int n, m;
    while (cin>>n>>m) {
        vector<pair<int, int>> table;
        unordered_map<int, int> sum_mp, product_mp;

        for (int i = 1; i <= n; ++i) {
            for (int j = i + 1; j <= n; ++j) {
                table.emplace_back(i, j);
                sum_mp[i + j]++;
                product_mp[i * j]++;
            }
        }
        vector<bool> useable(table.size(), true);
        for (int i = 0; i < m; ++i) {
            for (auto it = table.begin(); it != table.end(); ++it) {
                if (!(useable[it - table.begin()])) continue;
                int sum = it->first + it->second;
                int product = it->first * it->second;

                if (i % 2 == 0) {
                    if (sum_mp[sum] <= 1) {
                        sum_mp.erase(sum);
                        product_mp[product]--;
                        useable[it-table.begin()] = false;
                    }
                } else {
                    if (product_mp[product] <= 1) {
                        product_mp.erase(product);
                        sum_mp[sum]--;
                        useable[it-table.begin()] = false;
                    }
                }
            }
        }

        vector<pair<int, int>> res;
        if (m % 2 == 0) {
            for (const auto& p : table) {
                if(!useable[&p-&(table.front())])continue;
                if (sum_mp[p.first + p.second] == 1) {
                    res.push_back(p);
                }
            }
        } else {
            for (const auto& p : table) {
                if(!useable[&p-&(table.front())])continue;
                if (product_mp[p.first * p.second] == 1) {
                    res.push_back(p);
                }
            }
        }

        cout << res.size() << endl;
        for (const auto& p : res) {
            cout << p.first << " " << p.second << endl;
        }
    }
}