1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
#include <iostream>
#include "message.h"
#include "teatr.h"
using namespace std;

int n;
int k;

/*
int GetN() {
	cin >> n;
	return n;
}

int GetElement(int i){
	cin >> k;
	return k;
}
 
int MyNodeId(){
    return 0;
}

*/

int numbers[20000000];
int mergetemp[20000000];

// sorts the 'numbers' array;
// uses the 'mergetemp' array;
// returns number of inversions
long long int mergesort(int begin, int end){
	int mid = (begin + end) / 2;
	if (begin == end) {
		return 0;
	}
	long long int r1 = mergesort(begin, mid);
	long long int r2 = mergesort(mid+1, end);
	long long int invs = 0;
	
	int leftpos = begin;
	int rightpos = mid+1;
	int tempidx = begin;

	while(leftpos != mid+1 || rightpos != end+1){
		if(rightpos == end+1) {
			while(leftpos != mid+1){
				mergetemp[tempidx] = numbers[leftpos];
				leftpos++;
				tempidx++;
			}
		} else if(leftpos == mid+1){
			while(rightpos != end+1) {
				mergetemp[tempidx] = numbers[rightpos];
				rightpos++;
				tempidx++;
			}
		} else {
			if (numbers[leftpos] <= numbers[rightpos]){
				mergetemp[tempidx] = numbers[leftpos];
				leftpos++;
				tempidx++;
			} else {
				mergetemp[tempidx] = numbers[rightpos];
				rightpos++;
				tempidx++;
				invs += mid + 1 - leftpos;
			}
		}
	}
	
	for(int i = begin; i <= end; ++i){
		numbers[i] = mergetemp[i];
	}
	
	return r1 + r2 + invs;
}

int main(){
	int nodeid = MyNodeId();
	if(nodeid != 0){
		return 0;
	}
	n = GetN();
	for (int i = 0; i < n; ++i){
		numbers[i] = GetElement(i);
	}
	long long int res = mergesort(0, n-1);
	cout << res << endl;
	return 0;
}