hdoj 4911 Inversion 树状数组+离散化

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题意：给你n个可以重复的无序数列，问经过k次相邻交换后最少还有多少对逆序数

求逆序对可以用树状数组来做，对于重复的元素，可能在sort的时候交换编号

求和的时候要注意去重，还有一种方法就是稳定排序stable_sort

#include<string.h>#include<stdio.h>#include<algorithm>using namespace std;#define ll __int64#define N 100000+10struct ln{        int id,va;}in[N];int a[N],c[N];int n;int cmp(ln x,ln y){        return x.va<y.va;}int lowbit(int x) { return x&(-x);}void updata(int t,int value){        for(int i=t;i<=n;i+=lowbit(i))                c[i]+=value;}int getSum(int x){        int temp=0;        for(int i=x;i>=1;i-=lowbit(i))                temp+=c[i];        return temp;}int main(){        int k;        while(scanf("%d%d",&n,&k)!=EOF)        {                for(int i=1;i<=n;i++)                {                        scanf("%d",&in[i].va);                        in[i].id=i;                }                memset(c,0,sizeof(c));                sort(in+1,in+n+1,cmp);                a[in[1].id]=1;                for(int i=2;i<=n;i++)                {                        if(in[i].va!=in[i-1].va)                        a[in[i].id]=i;                        else                        a[in[i].id]=a[in[i-1].id];                }                ll ans=0;                for(int i=1;i<=n;i++)                {                   updata(a[i],1);                   printf("%d %d\n",getSum(a[i]),getSum(a[i]-1));                   int temp=i-getSum(a[i]-1);                   temp=temp-(getSum(a[i])-getSum(a[i]-1));                   ans+=temp;                }                if(ans-k<0) printf("0\n");                else                printf("%I64d\n",ans-k);        }        return 0;}

#include<string.h>#include<stdio.h>#include<algorithm>using namespace std;#define ll __int64#define N 100000+10struct ln{        int id,va;}in[N];int a[N],c[N];int n;int cmp(ln x,ln y){        return x.va<y.va;}int lowbit(int x) { return x&(-x);}void updata(int t,int value){        for(int i=t;i<=n;i+=lowbit(i))                c[i]+=value;}int getSum(int x){        int temp=0;        for(int i=x;i>=1;i-=lowbit(i))                temp+=c[i];        return temp;}int main(){        int k;        while(scanf("%d%d",&n,&k)!=EOF)        {                for(int i=1;i<=n;i++)                {                        scanf("%d",&in[i].va);                        in[i].id=i;                }                memset(c,0,sizeof(c));                stable_sort(in+1,in+n+1,cmp);                for(int i=1;i<=n;i++)                        a[in[i].id]=i;                ll ans=0;                for(int i=1;i<=n;i++)                {                   updata(a[i],1);                   int temp=i-getSum(a[i]);                   ans+=temp;                }                if(ans-k<0) printf("0\n");                else                printf("%I64d\n",ans-k);        }        return 0;}

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