拼多多-2020-08-02-后端笔试-第二题-思路和解法

创建一个骰子类，含有 上下左右前后 6 个属性，表示 6 个面。然后把骰子做标准化。我的方案是：把 1 放到 top 位置，然后把 左右前后 4 个面中的最小值放到 left 位置。然后把骰子转为字符串，存到 map 里计数即可。

#include <vector>
#include <iostream>
#include <unordered_map>
#include <algorithm>
#include <numeric>
#include <unordered_set>
#include <functional>
using namespace std;


// touzi: 骰子
struct Touzi{
    explicit Touzi(vector<int>& touzi){
        top = touzi[0];
        bottom = touzi[1];
        left = touzi[2];
        right = touzi[3];
        front = touzi[4];
        back = touzi[5];
    }

    void rotate(){
        // 把 1 放到 top
        if(bottom == 1){
            swap(top, bottom);
            swap(front, back);
        }else if(left == 1){
            int n = top;
            top = left;
            left = bottom;
            bottom = right;
            right = n;
        }else if(right == 1){
            int n = top;
            top = right;
            right = bottom;
            bottom = left;
            left = n;
        }else if(front == 1){
            int n = top;
            top = front;
            front = bottom;
            bottom = back;
            back = n;
        }else if(back == 1){
            int n = top;
            top = back;
            back = bottom;
            bottom = front;
            front = n;
        }

        // 把左右前后四个面中最小值放到 left 位置
        if(min(left, right) > min(front, back)){
            int n = left;
            left = front;
            front = right;
            right = back;
            back = n;
        }
        if(left > right){
            swap(left, right);
            swap(front, back);
        }

        // 经过上面两个变换，相同的骰子上下左右前后对应的值一定相等
    }

    string to_string() const{
        string s;
        s.push_back(top + '0');
        s.push_back(bottom + '0');
        s.push_back(left + '0');
        s.push_back(right + '0');
        s.push_back(front + '0');
        s.push_back(back + '0');
        return s;
    }

private:
    int top;
    int bottom;
    int left;
    int right;
    int front;
    int back;
};


void main(){
    int n;
    cin >> n;

    unordered_map<string, int> counter;
    for(int i=0;i<n;i++){
        vector<int> touzi(6, 0);
        for(int k = 0; k < 6; k++){
            int m;
            cin >>m;
            touzi[k] = m;
        }
        Touzi t(touzi);
        t.rotate();
        counter[t.to_string()] += 1;
    }

    vector<int> nums;
    for(auto & item : counter){
        nums.push_back(item.second);
    }
    // 降序排列
    sort(nums.begin(), nums.end(), greater<>());


    cout << nums.size() << '\n';
    for(int num: nums){
        cout << num << ' ';
    }
}