第k元素log(n)算法–划分树
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核心提示:#include<iostream>#include<cstdio>using namespace std;struct node{ int x,y; };node a[20000]; int d[20][100000],s[20][100000],n,m,x,
#include<iostream> #include<cstdio> using namespace std; struct node{ int x,y; }; node a[20000]; int d[20][100000],s[20][100000],n,m,x,y,z; bool cmp(const node a,const node b) { return a.x<b.x; } void buildtree(int h,int l ,int r) { if (l==r) return; int mid=(l+r)>>1,p=0; for (int i=l;i<=r;++i) { if (d[h][i]<=mid) { d[h+1][l+p]=d[h][i]; ++p;s[h][i]=p; } else { d[h+1][mid+1+i-l-p]=d[h][i]; s[h][i]=p; } } buildtree(h+1,l,mid); buildtree(h+1,mid+1,r); } int find(int h,int l,int r,int ll,int rr,int k) { if (ll==rr) return (d[h][ll]); int ls=0,rs=0; if (ll>l) ls=s[h][ll-1];rs=s[h][rr]; if (rs-ls>=k) return find(h+1,l,(l+r)>>1,l+ls,l+rs-1,k); else return find(h+1,((l+r)>>1)+1,r,((l+r)>>1)+1+ll-l-ls,((l+r)>>1)+rr-l+1-rs,k-(rs-ls)); } int main() { freopen("350.in","r",stdin); freopen("350.out","w",stdout); cin>>n>>m; for (int i=1;i<=n;++i) { cin>>a[i].x;a[i].y=i; } sort(a+1,a+n+1,cmp); for (int i=1;i<=n;++i) d[0][a[i].y]=i; buildtree(0,1,n); for (int i=1;i<=m;++i) { cin>>x>>y>>z; cout<<a[find(0,1,n,x,y,z)].x<<endl; } return 0; }
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