技術標籤：PAT甲級# set資料結構stlset演算法

題目連結

what

容易超時，給的時間只能遍歷一次

不信？熱乎的炮灰…

using namespace std;
#include<bits/stdc++.h>
set<int>store[51];
int N, M, n, a, p, q;
int  main() {
	cin >> N;
	for (int i = 1; i <= N; i++) {
		cin >> n;
		for (int j = 0; j < n; j++) {
			cin >> a;
 

			store[i].insert(a);
		}
	}
	cin >> M;
	for (int i = 0; i < M; i++) {
		cin >> p >> q;
		set<int>intersection,convergence;
		set_intersection(store[p].begin(), store[p].end(), store[q].begin(), store[q].end(), inserter(intersection, intersection.begin()));
		set_union(store[
 
p].begin(), store[p].end(), store[q].begin(), store[q].end(), inserter(convergence, convergence.begin()));
		cout << fixed << setprecision(1) << intersection.size()*1.0 / convergence.size() * 100 << "%" << endl;
	}
	return 0;
}

方法一

erase()，返回true \false

using namespace
 
 std;
#include <iostream>
#include <iomanip>
#include<set>
set<int>store[51], query;
int N, M, n, a, p, q;
int  main() {
	cin >> N;
	for (int i = 1; i <= N; i++) {
		cin >> n;
		for (int j = 0; j < n; j++) {
			cin >> a;
			store[i].insert(a);
		}
	}
	cin >> M;
	for (int i = 0; i < M; i++) {
		int cnt = 0;
		cin >> p >> q;
		query = store[q];
		int total= store[q].size();
		auto pointer = store[p].begin();
		for (pointer; pointer != store[p].end(); pointer++) {
			if (query.erase(*pointer) == false)total++;
			else cnt++;
		}
		cout << fixed << setprecision(1) << cnt*1.0/total* 100.0 << "%" << endl;
	}
	return 0;
}

方法二

find() ，返回給定值的迭代器，如果沒找到則返回end()。

using namespace std;
#include <iostream>
#include <iomanip>
#include<set>
set<int>store[51];
int N, M,n,a,p,q;
int  main() {
	cin >> N;
	for (int i = 1; i <= N; i++) {
		cin >> n;
		for (int j = 0; j < n; j++) {
			cin >> a;
			store[i].insert(a);
		}
	}
	cin >> M;
	for (int i = 0; i < M; i++) {
		double total= store[q].size();
		int cnt = 0;
		cin >> p >> q;
		auto pointer = store[p].begin();
		for (pointer; pointer != store[p].end(); pointer++) {
			if (store[q].find(*pointer) != store[q].end())cnt++;
			else total++;
		}
		cout << fixed << setprecision(1) << cnt / total * 100 <<"%"<< endl;
	}
	return 0;
}

方法三

insert()，返回值是pair<set::iterator,bool>

#include <iostream>
#include <iomanip>
#include<set>
set<int>store[51],query;
int N, M, n, a, p, q;
int  main() {
	cin >> N;
	for (int i = 1; i <= N; i++) {
		cin >> n;
		for (int j = 0; j < n; j++) {
			cin >> a;
			store[i].insert(a);
		}
	}
	cin >> M;
	for (int i = 0; i < M; i++) {
		int cnt = 0;
		cin >> p >> q;
		query = store[q];
		auto pointer = store[p].begin();
		for (pointer; pointer != store[p].end(); pointer++) {
			if (query.insert(*pointer).second == false)cnt++;
		}
		cout << fixed << setprecision(1) << cnt*1.0 / query.size() * 100.0 << "%" << endl;
	}
	return 0;
}