算阶,jdk和idea的安装

 用unordered_map存入，减少时间复杂度，然后通过题目比对求答案

#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;

int main() {
    int n, m;
    cin >> n;
    unordered_map<int, int> nums;  
    for (int i = 0; i < n; i++) {
        int num;
        cin >> num;
        nums[num]++;
    }

    cin >> m;
    vector<int> dy1(m + 1); 
    vector<int> dy2(m + 1);  

    for (int i = 1; i <= m; i++) {
        cin >> dy1[i];
    }
    for (int i = 1; i <= m; i++) {
        cin >> dy2[i];
    }
 
    int dynum = 1;  
    int maxHappy = 0;   
    int tt = 0;  

    for (int i = 1; i <= m; i++) {
        int happy = nums[dy1[i]]; 
        int _tt = nums[dy2[i]]; 
      
        if (happy > maxHappy || (happy == maxHappy && _tt > tt)) {
            dynum = i;
            maxHappy = happy;
            tt = _tt;
        }
    }

    cout << dynum << endl;
    return 0;
}

 排序加中位数为∣x−a∣+∣x−b∣+∣x−c∣+⋯+∣x−n∣∣x−a∣+∣x−b∣+∣x−c∣+⋯+∣x−n∣ 的最小值

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> stores(n);  
    for (int i = 0; i < n; i++) {
        cin >> stores[i];
    }

    sort(stores.begin(), stores.end());
    int mid = stores[n / 2];
 
    int sum = 0;
    for (auto& store : stores) {
        sum += abs(mid - store);
    }

    cout << sum << endl;
    return 0;
}

直接使用归并排序

#include <iostream>
#include <vector>
using namespace std;

 
long long mergesort(vector<int>& nums, int left, int right) {
    if (left >= right) return 0; 

    int mid = left + (right - left) / 2;
    long long cnt = 0;

    cnt += mergesort(nums, left, mid);
    cnt += mergesort(nums, mid + 1, right);

    vector<int> temp(right - left + 1);
    int i = left, j = mid + 1, k = 0;

    while (i <= mid && j <= right) {
        if (nums[i] <= nums[j]) {
            temp[k++] = nums[i++];
        }
        else {
            temp[k++] = nums[j++];
            cnt += mid - i + 1; 
        }
    }

    while (i <= mid) temp[k++] = nums[i++];
    while (j <= right) temp[k++] = nums[j++];

    for (int p = 0; p < k; p++) {
        nums[left + p] = temp[p];
    }

    return cnt;
}

int main() {
    int n;
    while (cin >> n && n != 0) {
        vector<int> nums(n);
        for (int i = 0; i < n; i++) {
            cin >> nums[i];
        }

        long long cnt = mergesort(nums, 0, n - 1);
        cout << cnt << endl;
    }
    return 0;
}