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HDU 1394 Minimum Inversion Number 线段树
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Minimum Inversion Number
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)Total Submission(s): 11345 Accepted Submission(s): 6967
Problem Description
The inversion number of a given number sequence a1, a2, ..., an is the number of pairs (ai, aj) that satisfy i < j and ai > aj.
For a given sequence of numbers a1, a2, ..., an, if we move the first m >= 0 numbers to the end of the seqence, we will obtain another sequence. There are totally n such sequences as the following:
a1, a2, ..., an-1, an (where m = 0 - the initial seqence)
a2, a3, ..., an, a1 (where m = 1)
a3, a4, ..., an, a1, a2 (where m = 2)
...
an, a1, a2, ..., an-1 (where m = n-1)
You are asked to write a program to find the minimum inversion number out of the above sequences.
For a given sequence of numbers a1, a2, ..., an, if we move the first m >= 0 numbers to the end of the seqence, we will obtain another sequence. There are totally n such sequences as the following:
a1, a2, ..., an-1, an (where m = 0 - the initial seqence)
a2, a3, ..., an, a1 (where m = 1)
a3, a4, ..., an, a1, a2 (where m = 2)
...
an, a1, a2, ..., an-1 (where m = n-1)
You are asked to write a program to find the minimum inversion number out of the above sequences.
Input
The input consists of a number of test cases. Each case consists of two lines: the first line contains a positive integer n (n <= 5000); the next line contains a permutation of the n integers from 0 to n-1.
Output
For each case, output the minimum inversion number on a single line.
Sample Input
10 1 3 6 9 0 8 5 7 4 2
Sample Output
16
在插入每个数的同时查询(x[i]-n-1)的数出现过的个数然后更新
#include<cstdio> #include<cstring> #include<algorithm> #define MAXN 5555 using namespace std; int sum[MAXN<<2]; int x[MAXN]; void pushup(int rt) { sum[rt]=sum[rt<<1]+sum[rt<<1|1]; } int query(int L,int R,int l,int r,int rt) { if(L<=l&&r<=R) { return sum[rt]; } int cnt=0; int mid=(l+r)>>1; if(L<=mid) cnt=query(L,R,l,mid,rt<<1); if(R>mid) cnt+=query(L,R,mid+1,r,rt<<1|1); return cnt; } void update(int q,int l,int r,int rt) { if(l==r) { sum[rt]=1; return ; } int mid=(l+r)>>1; if(q<=mid) update(q,l,mid,rt<<1); else update(q,mid+1,r,rt<<1|1); pushup(rt); } int main() { int n,i,xxx,ans; while(scanf("%d",&n)!=EOF) { for(i=0;i<n<<2;i++) { sum[i]=0; } xxx=0; for(i=0;i<n;i++) { scanf("%d",&x[i]); xxx+=query(x[i],n-1,0,n-1,1); // for(int j=1;j<=16;j++) //{ // printf("%d ",sum[j]); //} //puts(""); //printf("1\n"); update(x[i],0,n-1,1); //for(int j=1;j<=16;j++) //{ // printf("%d ",sum[j]); //} //puts(""); } ans=xxx; for(i=0;i<n;i++) { xxx+=n-x[i]-x[i]-1; ans=min(ans,xxx); } printf("%d\n",ans); } return 0; }
HDU 1394 Minimum Inversion Number 线段树
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