[gcj] Asking for help for Round 1A Pylons

[Wing-chung Leung]

Dear all,

   I'm unable to get the output pass Test Set 2, even if it passed my own 
validation.

   I would appreciate if anyone can point out what's my mistake, especially 
those in my validator code. Thanks!

Regards,
WC Leung.


// Compile with MinGW-64 in MSYS2

#include <stdint.h>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <string>
#include <queue>
#include <unordered_set>
#include <vector>

using namespace std;

vector<pair<int, int>> result;

void build2(int cols, int startrow) {
    for (int i = 0; i < 2; ++i) {
        int r = i;
        int c = 0;
        for (int j = 0; j < cols; ++j) {
            result.emplace_back(r+1+startrow, c+1);

            c += 2;
            c %= cols;
            if (c == 0) c = 1;
            r += 1;
            r %= 2;
        }
    }
}

void build3(int cols, int startrow) {
    if (cols % 3 == 0) {
        for (int i = 0; i < cols; ++i) {
            int r = 0;
            int c = i;
            for (int j = 0; j < 3; ++j) {
                result.emplace_back(r+1+startrow, c+1);

                c += 2;
                c %= cols;
                r += 1;
                r %= 3;
            }
        }

    } else {
        int r = 0;
        int c = 0;
        for (int i = 0; i < cols; ++i) {
            for (int j = 0; j < 3; ++j) {
                result.emplace_back(r+1+startrow, c+1);

                c += 2;
                c %= cols;
                r += 1;
                r %= 3;
            }
            
            c += (cols - 3);
            c %= cols;
        }
    }    
}

void build4(int rows) {
    vector<int> start = {3, 0, 1, 2};
    for (int c : start) {
        for (int r = 0; r < rows; ++r) {
            result.emplace_back(r+1, c+1);
            c += 2;
            c %= 4;
        }
    }
}

void solve(int caseNo) {
    std::cout << "Case #" << caseNo << ": ";

    int rows, cols;
    cin >> rows >> cols;
    
    bool reverse = rows > cols;
    if (reverse)
        swap(rows, cols);

    int length = cols;
    int width = rows;
    if (width == 1 && length == 1) {
        cout << "POSSIBLE\n1 1\n";
        return;
    } else if (width == 1 || (width == 2 && length <= 4) || (width == 3 && 
length < 4)) {
        cout << "IMPOSSIBLE\n";
        return;
    }
    
    result.clear();

    cout << "POSSIBLE\n";
    if (cols == 4) {
        build4(rows);
    } else {
        for (int r = 0; r < rows; r += 2) {
            if (rows - r == 3) {
                build3(cols, r);
                break;
            }
            build2(cols, r);
        }
    }

    unordered_set<int> played;
    pair<int, int> prev{-1000, -1};
    for (pair<int, int> item : result) {
        if (item.first < 1 || item.first > rows || item.second < 1 || 
item.second > cols) {
            cerr << "out of range: " << rows << " " << cols << '\n';
            break;
        }

        if (reverse)
            swap(item.first, item.second);
        
        int num = item.first * 100 + item.second;
        if (played.count(num) == 1) {
            cerr << "repeat!" << rows << " " << cols << '\n';
            break;
        }

        played.insert(num);

        if (item.first == prev.first || item.second == prev.second || 
            item.first + item.second == prev.first + prev.second ||
            item.first - item.second == prev.first - prev.second) {
            cerr << "bad play: " << rows << " " << cols << '\n';
            break;
        }

        cout << item.first << ' ' << item.second << '\n';
    }
    
    cerr << '#';
    if ((reverse ? rows : cols) == 20) cerr << '\n';
}

int main(int argc, char** argv) {
    int N;
    std::cin >> N;
    
    std::string str;
    std::getline(std::cin, str);

    for (int i = 0; i < N; ++i) {
        solve(i + 1);
    }

    return 0;
}

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