PTA乙级 （1059 C语言竞赛 (20分)（map.find()、vector中的find））

一、vector中的find

注意find不属于vector的成员，而存在于算法中，应加上头文件#include <algorithm>

#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;
int main( )
{
    vector<int> L;
    L.push_back( 1 );
    L.push_back( 2 );
    L.push_back( 3 );
    L.push_back( 4 );
    L.push_back( 5 );
    vector<int>::iterator result = find( L.begin( ), L.end( ), 3 ); //查找3
    if ( result == L.end( ) ) 
        cout << "No" << endl;
    else 
        cout << "Yes" << endl;
}

二、map.find()和map.count()方法

使用find，返回的是被查找元素的位置，没有则返回map.end();

使用count，返回的是被查找元素的个数。如果有，返回1；否则，返回0。注意，map中不存在相同元素，所以返回值只能是1或0.

// map::find
#include <iostream>
#include <map>

int main ()
{
  std::map<char,int> mymap;
  std::map<char,int>::iterator it;

  mymap['a']=50;
  mymap['b']=100;
  mymap['c']=150;
  mymap['d']=200;

  it = mymap.find('b');
  if (it != mymap.end())
    mymap.erase (it);

  // print content:
  std::cout << "elements in mymap:" << '
';
  std::cout << "a => " << mymap.find('a')->second << '
';
  std::cout << "c => " << mymap.find('c')->second << '
';
  std::cout << "d => " << mymap.find('d')->second << '
';

  return 0;
}

#include<string>
#include<cstring>
#include<iostream>
#include<map>
#include<algorithm>
using namespace std;
int main(){
    map<string,int> mp;
    mp.insert(make_pair("a",1));
    mp.insert(make_pair("b",2));
    map<string,int>::iterator it;
    cout<<mp.count("a")<<endl;
    mp.insert(make_pair("a",2));
    it=mp.find("a");
    if(it==mp.end()) cout<<"No!"<<endl;
    else cout<<it->second<<endl;
    cout<<mp.count("a")<<endl;
    return 0;
}

三、1059 C语言竞赛 (20分)

https://pintia.cn/problem-sets/994805260223102976/problems/994805269828059136

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <map>
bool is_prime(int a)
{
    int i;
    for(i=2;i<=(int)(sqrt(a));i++)
    {
        if(a%i==0) return false;
    }
    if(i>(int)(sqrt(a))) return true; 
}
using namespace std;
int main()
{
    int n,k;
    string str;
    bool flag[10002]={false};
    cin>>n;
    map<string,int> mp;
    for(int i=1;i<=n;i++) 
    {
        cin>>str;
        mp[str]=i;
        flag[i]=false;
    }
    cin>>k;
    for(int i=0;i<k;i++)
    {
        cin>>str;
        if(mp.find(str)!=mp.end())
        {
            if(flag[mp[str]]==true) cout<<str<<": Checked
";
            else{
                flag[mp[str]]=true;
                if(mp[str]==1) cout<<str<<": Mystery Award
";
                else if(is_prime(mp[str])) cout<<str<<": Minion
";
                else cout<<str<<": Chocolate
"; 
            }
        }
        else cout<<str<<": Are you kidding?
";
    }
    return 0;
}