獲得第k小元素

分治，關鍵是用到快拍的時候的partation函數

#include<iostream>#include<hash_map>#include<string>#include<iterator>#include<algorithm>using namespace std;const int maxn=100;int tab[maxn];template<class T>int random_partition(T* tab,int p,int q){if(p==q)return p;//select one pos and then swap this postion element with the firstint pos=rand()%(q-p)+p;swap(tab[p],tab[pos]);int left=p+1,right=q;while(left<=right){while(tab[left]<=tab[p]&&left<=q)++left;while(tab[right]>=tab[p]&&right>=p+1)--right;if(left<right)swap(tab[left],tab[right]);}swap(tab[p],tab[right]);return right;}int selectKthMin(int* tab,int p,int q,int k){if(p==q)return tab[p];int r=random_partition<int>(tab,p,q);int pos=r-p+1;if(pos==k)return tab[r];if(pos>k)return selectKthMin(tab,p,r-1,k);return selectKthMin(tab,r+1,q,k-pos);}int main(){ int n=8;int tab[]={0,10,2,13,4,5,6,27};for(int i=1;i<=7;i++)cout<<selectKthMin(tab,1,7,i)<<endl;return 0;}