POJ 3349.Snowflake Snow Snowflakes

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题目:http://poj.org/problem?id=3349

AC代码(C++):

#include <iostream>#include <algorithm>#include <stdio.h>#include <vector>#include <queue>#include <math.h>#include <string>#include <string.h>#include <bitset>#define INF 0xfffffff#define MAXN 1200010#define prime 1200007using namespace std;struct NODE{int num[6];int next;};NODE node[MAXN];int hash[MAXN];int nodecnt;bool cmp(int* num1, int* num2){for(int i = 0; i < 6; i++){if(num1[i]!=num2[i])return false;}return true;}int getHash(int* num){return (num[0]%prime + num[1]%prime + num[2]%prime + num[3]%prime + num[4]%prime + num[5])%prime;}void insertHash(int* num, int key){for(int i = 0; i < 6; i++)node[nodecnt].num[i] = num[i];node[nodecnt].next = hash[key];hash[key] = nodecnt;nodecnt++;}bool searchHash(int* num){int key = getHash(num);int next = hash[key];while(next!=-1){if(!cmp(num,node[next].num)){next = node[next].next;}else return true;}insertHash(num,key);return false;}int main(){int n;cin>>n;bool flag = false;nodecnt = 0;for(int i = 0; i < MAXN; i++)hash[i] = -1;while(n--){int num[2][12];for(int i = 0; i < 6; i++){scanf("%d",&num[0][i]);num[0][i+6] = num[0][i];num[1][5-i] = num[0][i];num[1][5-i+6] = num[0][i];}if(flag)continue;for(int i = 0; i < 6; i++){if(searchHash(num[0]+i)||searchHash(num[1]+i)){flag = true;break;}}}if(flag)cout<<"Twin snowflakes found.";else cout<<"No two snowflakes are alike.";}

总结: 数字哈希. 顺逆时针和顺序需要注意下, 还有就是这题时间很紧, 能优化的地方要优化下. 其实我这个代码还有待改善, 首先是时间太紧3719ms差点TLE, 其次如果输入1 1 1 1 1 2这样的雪花就会直接认为有相同, 因为在insert完顺时针i = 0的时候已经插入了1 1 1 1 1 2, 在search逆时针i = 1时直接搜到了刚才插入的1 1 1 1 1 2, 所以认为是相同的.

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