蓝桥杯历年试题 小朋友排队

#include <iostream>
#include <cstdio>
#include <string>
#include <cmath>
#include <map>
#include <algorithm>
#define LL long long int
#define N 100005
using namespace std;
int cmp(int a,int b)
{
    if(a==b) return 0;
    return a<b?-1:1;
}
struct node
{
    int num;
    int ang;

};
LL ans[N];
void MergeArr(node num[], int left, int mid, int right)
{
    node AL[N], AR[N];
    int lenl=mid-left+1,lenr=right-mid;
    for (int i = 0;i < lenl;i++)
        AL[i] = num[left + i];
    for (int i = 0;i < lenr;i++)
        AR[i] = num[mid + 1 + i];
    int j = 0, k = 0,pos=left;
    int tempNum=-1,tempCnt=0;
    while (j < lenl&&k < lenr)
    {
        int fix=cmp(AL[j].num, AR[k].num);
        if (fix<=0)
        {
            num[pos++] = AL[j++],num[pos-1].ang+=k;
            if(num[pos-1].num==tempNum)
                num[pos-1].ang-=tempCnt;
        }
        //else if(fix==-1) num[pos++] = AL[j++];
        else
            num[pos++] = AR[k++],num[pos-1].ang+=mid-(left+j)+1;//关键步骤
        if(fix>0)
        {
            if(num[pos-1].num==tempNum)
                tempCnt++;
            else
                tempNum=num[pos-1].num,tempCnt=1;
        }

    }
    while (j < lenl)
    {
        num[pos++] = AL[j++];
        num[pos-1].ang+=k;
        if(num[pos-1].num==tempNum)
            num[pos-1].ang-=tempCnt;
    }
    while (k < lenr)
        num[pos++] = AR[k++];
}
void MergeSort(node num[], int left, int right)
{
    if (left < right)
    {
        int mid = (right + left) / 2;
        MergeSort(num, left, mid);
        MergeSort(num, mid+1, right);
        MergeArr(num, left, mid, right);
    }
}
LL mat(LL num)
{
    return num*(num+1)/2;
}
node num[N];
int n;
int main()
{
    cin.sync_with_stdio(false);
    while(cin>>n)
    {
        LL fuck=0;
        for(int i=0;i<n;i++)
            cin>>num[i].num,num[i].ang=0;
        MergeSort(num,0,n-1);
        for(int i=0;i<n;i++)
            fuck+=mat(num[i].ang);

        cout<<fuck<<endl;
    }
    return 0;
}