uva11549 <Floyd判圈法>

来源：互联网发布：python sys.exit用法编辑：程序博客网时间：2024/05/16 10:49

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#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <set>#include <map>#include <string>#include <cmath>#include <climits>#include <cstdlib>#include <ctime>using namespace std;char buff[20];int next(int n,int k){if(!k)  return 0;long long  k2 = (long long ) k * k;memset(buff,0,sizeof(buff));sprintf(buff,"%lld",k2);if(strlen(buff) < n) n = strlen(buff);k2 = 0;for(int i = 0; i < n;i++){k2 = k2 *10 + buff[i] - '0';}return k2;}int main(){int t;cin >> t;while(t--){int n,k;scanf("%d%d",&n,&k);int k1 = k;int k2 = k;int ans = k;do{k1 = next(n,k1);k2 = next(n,k2);if(k2 > ans) ans = k2;k2 = next(n,k2);if(k2 > ans) ans = k2;}while(k1 != k2);printf("%d\n",ans);}return 0;}

该题的重点不在于题目而是在于该题中才用的求循环节的（圈）的方法。该题中<pre name="code" class="cpp"><span style="white-space:pre"></span>int k1 = k;int k2 = k;int ans = k;do{k1 = next(n,k1);k2 = next(n,k2);if(k2 > ans) ans = k2;k2 = next(n,k2);if(k2 > ans) ans = k2;}while(k1 != k2);

这一段中k1,k2均是从k出发，每次但是每次求得时候k2 总是更新两次但是k1每次都是执行一次。这样的话就如果k1能追上k2的时候说明这中间有圈。就好像两个人在一个跑道上跑，一个人的速度是另外一个人的两倍，如果两个人相遇啦那就说明跑道有圈

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