POJ3344 Snowflake Snow Snowflakes （hash）

最新推荐文章于 2020-09-06 17:13:10 发布

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本文介绍了一个用于判断雪花是否相同的程序实现。通过读取输入文件中的雪花数据，并使用哈希表来快速查找可能完全相同的雪花对。对于每一对潜在相同的雪花，程序会进行详细的比较以确定它们是否真的相同。

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You may have heard that no two snowflakes are alike. Your task is to write a program to determine whether this is really true. Your program will read information about a collection of snowflakes, and search for a pair that may be identical. Each snowflake has six arms. For each snowflake, your program will be provided with a measurement of the length of each of the six arms. Any pair of snowflakes which have the same lengths of corresponding arms should be flagged by your program as possibly identical.

Input

The first line of input will contain a single integer n, 0 < n ≤ 100000, the number of snowflakes to follow. This will be followed by n lines, each describing a snowflake. Each snowflake will be described by a line containing six integers (each integer is at least 0 and less than 10000000), the lengths of the arms of the snow ake. The lengths of the arms will be given in order around the snowflake (either clockwise or counterclockwise), but they may begin with any of the six arms. For example, the same snowflake could be described as 1 2 3 4 5 6 or 4 3 2 1 6 5.

Output

If all of the snowflakes are distinct, your program should print the message:
No two snowflakes are alike.
If there is a pair of possibly identical snow akes, your program should print the message:
Twin snowflakes found.

Sample Input

2
1 2 3 4 5 6
4 3 2 1 6 5

Sample Output

Twin snowflakes found.

把雪花长度求和再mod一个大质数（999983为最大的六位质数），存入hash

用动态数组存hash表中求和取mod后相等的雪花标号

比较两个雪花时，先找起始位置，然后分别顺时针、逆时针比较

#include <cstdio>
#include <iostream>
#include <vector>
#include <cstring>
#include <string>
#define N 999983
#define M 100005
using namespace std;
vector <int> G[N];
int n;
int a[M][8];

bool cmp(int x,int y){
    for (int i = 0;i < 6;i++){
        if (a[y][i] == a[x][0]){
            bool flag = false;
            for (int j = 1;j < 6;j++){
                int t = (j + i) % 6;
                if (a[y][t] != a[x][j]) {flag =true; break;}
            }
            if (!flag) return 1;
            flag = false;
            for (int j = 1;j < 6;j++){
                int t = (i + 6 - j) % 6;
                if (a[y][t] != a[x][j]) {flag = true; break;}
            }
            if (!flag) return 1;
        }
    }
    return 0;
}

int main(){
    scanf("%d",&n);
    bool flag = false;
    for (int i = 0;i < n;i++){
        int sum = 0;
        for (int j = 0;j < 6;j++){
            scanf("%d",&a[i][j]);
            sum += a[i][j];
            sum %= N;
        }
        if (flag) continue;
        if (G[sum].size() == 0){
            G[sum].push_back(i);
            continue;
        }
        for (int j = 0;j < G[sum].size();j++){
            if (cmp(G[sum][j],i)){
                flag = true;
                break;
            }
        }
        if (!flag) G[sum].push_back(i);
    }
    if (flag) printf("Twin snowflakes found.\n");
        else printf("No two snowflakes are alike.\n");
    return 0;
}