标签：ensure number sed 遇到 nes push 系统 iostream ram
When register on a social network, you are always asked to specify your hobbies in order to find some potential friends with the same hobbies. A social cluster is a set of people who have some of their hobbies in common. You are supposed to find all the clusters.
Each input file contains one test case. For each test case, the first line contains a positive integer N (≤1000), the total number of people in a social network. Hence the people are numbered from 1 to N. Then N lines follow, each gives the hobby list of a person in the format:
K?i??: h?i??[1] h?i??[2] ... h?i??[K?i??]
where K?i?? (>0) is the number of hobbies, and h?i??[j] is the index of the j-th hobby, which is an integer in [1, 1000].
For each case, print in one line the total number of clusters in the network. Then in the second line, print the numbers of people in the clusters in non-increasing order. The numbers must be separated by exactly one space, and there must be no extra space at the end of the line.
8
3: 2 7 10
1: 4
2: 5 3
1: 4
1: 3
1: 4
4: 6 8 1 5
1: 4
3
4 3 1这道题考察并查集。
开始遇到了数组越界的问题，后来调试发现是最近考研复习计算机系统基础遇到的一个知识点：
1 for (i = 1; i < 1001; i++) 2 { 3 for (j = 0; j < hobby[i].size() - 1; j++) 4 _union(hobby[i][j], hobby[i][j + 1]); 5 }
我开始是这么写的，看似不会发生数组越界的问题，但是因为hobby[i].size()是无符号数unsigned型，当hobby[i].size()等于0时，减去1就成了无符号数2^32-1，所以发生了越界。
看来了解底层的一些原理确实很重要，usigned型要慎用。
#include <iostream> #include <vector> #include <algorithm> using namespace std; vector<vector<int>> hobby(1001); vector<int> father(1001, -1); void _union(int i, int j); int find(int i); int main() { int N; cin >> N; int i, j, k, t; char c; for (i = 1; i <= N; i++) { cin >> k >> c; for (j = 0; j < k; j++) { cin >> t; hobby[t].push_back(i); } } for (i = 1; i < 1001; i++) { for (j = 1; j < hobby[i].size(); j++) _union(hobby[i][j], hobby[i][j - 1]); } vector<int> cluster; for (i = 1; i <= N; i++) { if (father[i] < 0) cluster.push_back(-father[i]); } sort(cluster.begin(), cluster.end()); cout << cluster.size() << endl << cluster[cluster.size() - 1]; for (i = cluster.size() - 2; i >= 0; i--) cout << " " << cluster[i]; return 0; } void _union(int i, int j) { int a = find(i); int b = find(j); if (a == b) return; if (father[a] < father[b]) { father[a] += father[b]; father[b] = a; } else { father[b] += father[a]; father[a] = b; } } int find(int i) { while (father[i] > 0) i = father[i]; return i; }
标签：ensure number sed 遇到 nes push 系统 iostream ram
原文地址：https://www.cnblogs.com/lxc1910/p/9690539.html
