一、视频讲解

[蓝桥杯]真题讲解：班级活动（贪心）

二、正解代码

1、C++

#include<bits/stdc++.h>
using namespace std;int main(){int n; cin >> n;vector<int>a(n);map<int,int>st;for(int i = 0; i < n; i ++) {cin >> a[i];st[a[i]] ++;}int ans = 0;int c1 = 0, c2 = 0;for(auto x: st) {if(x.second > 2){c2 += (x.second - 2);}else if(x.second == 1) {c1 += 1;}}if(c1 < c2){cout << c2 << endl;}else {cout << c2 + (c1 - c2) / 2 << endl;}
}

2、python3

n = int(input())
a = list(map(int, input().split()))
st = {}
for x in a:if x not in st:st[x] = 1else:st[x] += 1ans, c1, c2 = 0, 0, 0
for x, y in st.items():if y > 2:c2 += (y - 2)elif y == 1:c1 += 1if c1 < c2:print(c2)
else:print(c2 + (c1 - c2) // 2)

3、Java

import java.util.*;public class Main {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();List<Integer> a = new ArrayList<>();Map<Integer, Integer> st = new HashMap<>();for(int i = 0; i < n; i ++) {int x = sc.nextInt();a.add(x);if(st.get(x) != null)st.put(x, st.get(x) + 1);elsest.put(x, 1);}int ans = 0, c1 = 0, c2 = 0;for(Map.Entry<Integer, Integer> x: st.entrySet()){if(x.getValue() > 2) {c2 += x.getValue() - 2;}else if(x.getValue() == 1) {c1 += 1;}}if(c1 < c2) {System.out.println(c2);}else{System.out.println(c2 + (c1 - c2) / 2);}}
}