poj 2299 Ultra-QuickSort

和小朋友排队时一样的题，线段树+离散化+逆序数，注意求的是交换几次，最后结果除2.

<span style="font-size:18px;">#include<iostream>#include<stdio.h>#include<math.h>#include<string.h>#include<vector>#include<list>#include<algorithm>using namespace std;#define MAX 500010#define lson l,m,level*2#define rson m+1,r,level*2+1long long a[MAX];long long b[MAX];long long insert(long long l,long long r,long long level,long long x);long long found(long long x);struct node{long long x;long long l;long long h;}num[MAX];long long n;long long tree[MAX*5];int main(){scanf("%I64d",&n);while(n){ for(long long i=1;i<=n;i++){ scanf("%I64d",&a[i]); b[i] = a[i]; num[i].h = 0; } //离散化  sort(b+1,b+1+n); for(long long i=1;i<=n;i++){ long long t = found(a[i]); a[i] = t; num[t].x = i; b[t]--; } //线段树插入  memset(tree,0,sizeof(tree)); long long sum = 0; for(long long i=1;i<=n;i++){ num[a[i]].h = insert(1,n,1,a[i]);//点插入（按照原顺序，计算比该点大的数的数目）  num[a[i]].l = a[i] - (num[a[i]].x - num[a[i]].h); sum += num[a[i]].h + num[a[i]].l; }  printf("%I64d\n",sum/2);scanf("%I64d",&n);}return 0;}long long insert(long long l,long long r,long long level,long long x){if(l==r&&l==x){tree[level] = 1;return 0;//注意该点不计入 }long long m = (l+r)>>1;long long temp;if(x<=m){temp = insert(lson,x);temp += tree[level*2+1];//加上比他大的数 }else if(x>m){temp = insert(rson,x);}tree[level] = tree[level*2] + tree[level*2+1];//更新tree return temp;}//二分 long long found(long long x){long long l = 1,r = n;long long mid;while(l<r){mid = (l+r)/2;if(b[mid]==x){if(b[mid-1]!=x)return mid;elser = mid-1;}else if(b[mid]>x){r = mid-1;}else if(b[mid]<x){l = mid+1;}}return l;}</span>