学步园

因为只能交换相邻的两个数，其他数和这两个的数的相对位置没有影响，所以逆序数只会改变0，-1，+1，因为要求minimum，所以每次都让逆序数-1，因为操作no more than k times，当顺序的时候停止操作即可。

WA了好久还以为是模板错了，最后发现是因为把10W敲成了10000。。。以后直接写1e5+10好了==

#include<iostream>
#include<stdio.h>
#include<cstdio>
#include<stdlib.h>
#include<vector>
#include<string>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<stack>
#include<queue>
#include <ctype.h>
#include<map>
#include<time.h>
using namespace std;
//hdu 4911

const int maxn=100010;
long long a[maxn];
int n;
long long k;
long long cnt;
long long b[maxn];
long long c[maxn];
long long merge_sort (int l, int r)
{
    if (l == r)
        return 0;
    int mid = (l + r) / 2;
    long long ret = merge_sort(l, mid) + merge_sort(mid+1, r);
    int mvl = l, mvr = mid+1, mv = l;
    while (mvl <= mid || mvr <= r) {
        if (mvr > r || (mvl <= mid && a[mvl] <= a[mvr])) {
            b[mv++] = a[mvl++];
        } else {
            ret += mid - mvl + 1;
            b[mv++] = a[mvr++];
        }
    }
    for (int i = l; i <= r; i++)
        a[i] = b[i];
    return ret;
}

void mergesort(int l,int r)
{
    int mid,i,j,tmp;
    if(r>l+1)
    {
        mid=(l+r)/2;
        mergesort(l,mid);
        mergesort(mid,r);
        tmp=l;
        for(i=l,j=mid;i<mid&&j<r;)
        {
            if(a[i]>a[j])
            {
                c[tmp++]=a[j++];
                cnt+=mid-i;
            }
            else c[tmp++]=a[i++];
        }
        if(j<r) for(;j<r;++j) c[tmp++]=a[j];
        else for(;i<mid;++i) c[tmp++]=a[i];
        for(i=1;i<r;++i) a[i]=c[i];
    }
}

int main()
{
    freopen("input.txt","r",stdin);
   //  freopen("data.txt","r",stdin);
    // freopen("out1.txt","w",stdout);
    while(scanf("%d %I64d",&n,&k)!=EOF)
    {
        memset(c,0,sizeof(c));
        memset(a,0,sizeof(a));
        memset(b,0,sizeof(b));
        cnt=0;
        for(int i=0;i<n;i++)
        {
            scanf("%I64d",&a[i]);
        }

      // cnt=merge_sort(1,n);
        cnt=merge_sort(0,n-1);
        long long ans=max(0LL,cnt-k);
        printf("%I64d\n",ans);
    }

    return 0;
}