学步园

Description

In this problem, you have to analyze a particular sorting algorithm. The algorithm processes a sequence of n distinct integers by swapping two adjacent sequence elements
until the sequence is sorted in ascending order. For the input sequence
9 1 0 5 4 ,

Ultra-QuickSort produces the output
0 1 4 5 9 .

Your task is to determine how many swap operations Ultra-QuickSort needs to perform in order to sort a given input sequence.

Input

Output

Sample Input

5
9
1
0
5
4
3
1
2
3
0

Sample Output

6
0

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn = 500010;
long long cnt = 0;
int a[maxn], t[maxn];

void merge_sort(int *A, int x, int y, int* T) {//contain [x,y]
    if(x==y) return ;
   // printf("x = %d, y = %d\n", x, y);
    if(y-x>=1) {
        int m = (x+y)/2;
        int p = x, q = m+1, i = x;
        merge_sort(A, x, m, T);
        merge_sort(A, m+1, y, T);
        while(p <= m || q <= y) {
            if(p<=m && q<=y && A[p]<=A[q]) {
                T[i++] = A[p++];
            }
            if(p<=m && q<=y && A[p]>A[q]) {
                cnt =  cnt + (m-p+1);
             //   printf("cnt = %d\n", cnt);
                T[i++] = A[q++];
            }
            while(q>y && p<=m) {
                T[i++] = A[p++];
            }
            while(p>m && q<=y) {
                T[i++] = A[q++];
            }
        }
        for( i = x; i <= y; i++) {
            A[i] = T[i];
        }
    }
}

int main()
{
    int n;
    while((scanf("%d", &n) != EOF) && n) {
        for(int i = 0; i < n; i++) {
            scanf("%d", &a[i]);
        }
        merge_sort(a, 0, n-1, t);
        printf("%lld\n", cnt);
        cnt = 0;
    }
    return 0;
}

/**********************
5
9 1 0 5 4
8
9 1 0 5 4 3 8 7
**************/